.  STEVENS, J., filed a dissenting opinion, in which BRENNAN and MARSHALL, JJ., joined, post, p.  431 U. S. 625MR. JUSTICE REHNQUIST delivered the opinion of the Court.Customs officials, acting with "reasonable cause to suspect" a violation of customs laws, opened for inspection incoming international letter-class mail without first obtaining a search warrant.  A divided Court of Appeals for the District of Columbia Page 431 U. S. 608 Circuit held, contrary to every other Court of Appeals which has considered the matter, [Footnote 1] that the Fourth Amendment forbade the opening of such mail without probable cause and a search warrant.  176 U.S.App.D.C. 67, 538 F.2d 415.  We granted the Government's petition for certiorari to resolve this Circuit conflict.  429 U.S. 815.  We now reverse.ICharles W. Ramsey and James W. Kelly jointly commenced a heroin-by-mail enterprise in the Washington, D.C. area.  The process involved their procuring of heroin, which was mailed in letters from Bangkok, Thailand, and sent to various locations in the District of Columbia area for collection.  Two of their suppliers, Sylvia Bailey and William Ward, who were located in West Germany, were engaged in international narcotics trafficking during the latter part of 1973 and the early part of 1974.  West German agents, pursuant to court-authorized electronic surveillance, intercepted several trans-Atlantic conversations between Bailey and Ramsey during which their narcotics operation was discussed.  By late January, 1974, Bailey and Ward had gone to Thailand.  Thai Page 431 U. S. 609 officials, alerted to their presence by West German authorities, placed them under surveillance.  Ward was observed mailing letter-sized envelopes in six different mail boxes; five of these envelopes were recovered; and one of the addresses in Washington, D.C. was later linked to respondents.  Bailey and Ward were arrested by Thai officials on February 2, 1974; among the items seized were eleven heroin-filled envelopes addressed to the Washington, D.C. area, and later connected with respondents.Two days after this arrest of Bailey and Ward, Inspector George Kallnischkies, a United States customs officer in New York City, without any knowledge of the foregoing events, inspecting a sack of incoming international mail from Thailand, spotted eight envelopes that were bulky and which he believed might contain merchandise. [Footnote 2]  The envelopes, all of which appeared to him to have been typed on the same typewriter, were addressed to four different locations in the Washington, D.C. area.  Inspector Kallnischkies, based on the fact that the letters were from Thailand, a known source of narcotics, and were "rather bulky," suspected that the envelopes might contain merchandise or contraband, rather than correspondence.  He took the letters to an examining area in the post office, and felt one of the letters:  it "felt like there was something in there, in the envelope.  It was not just plain paper that the envelope is supposed to contain."  He weighed one of the envelopes, and found it weighed 42 grams, some three to six times the normal weight of an airmail letter.  Inspector Kallnischkies then opened that envelope: [Footnote 3]"In there I saw some cardboard and between the cardboard, if I recall, there was a plastic bag containing a Page 431 U. S. 610 white powdered substance, which, based on experience, I knew from Thailand would be heroin.""I went ahead and removed a sample.  Gave it a field test, a Marquis Reagent field test, and I had a positive reaction for heroin."App. 32.  He proceeded to open the other seven envelopes, which, "in a lot of ways, were identical"; examination revealed that at least the contents were in fact identical:  each contained heroin.The envelopes were then sent to Washington in a locked pouch, where agents of the Drug Enforcement Administration, after obtaining a search warrant, opened the envelopes again and removed most of the heroin. [Footnote 4]  The envelopes were then resealed, and six of them were delivered under surveillance.  After Kelly collected the envelopes from the three different addressees, rendezvoused with Ramsey, and gave Ramsey a brown paper bag, federal agents arrested both of them.  The bag contained the six envelopes with heroin, $1,100 in cash, and "cutting" material for the heroin.  The next day, in executing a search upon warrant of Ramsey's residence, agents recovered, inter alia, two pistols.Ramsey and Kelly were indicted, along with Bailey and Ward, in a 17-count indictment. [Footnote 5]  Respondents moved to Page 431 U. S. 611 suppress the heroin and the two pistols. [Footnote 6]  The District Court denied the motions, and, after a bench trial on the stipulated record, respondents were found guilty and sentenced to imprisonment for what is in effect a term of 10 to 30 years.  The Court of Appeals for the District of Columbia Circuit, one judge dissenting, reversed the convictions, holding that the "border search exception to the warrant requirement" applicable to persons, baggage, and mailed packages did not apply to the routine opening of international letter mail, and held that the Constitution requires that "before international letter mail is opened, a showing of probable cause be made to and a warrant secured from a neutral magistrate."  176 U.S.App.D.C. at 73, 538 F.2d  at 421. [Footnote 7]IICongress and the applicable postal regulations authorized the actions undertaken in this case.  Title 19 U.S.C. § 482, a recodification of Rev.Stat. § 3061, and derived from § 3 of the Act of July 18, 1866, 14 Stat. 178, explicitly deals with the search of an "envelope":"Any of the officers or persons authorized to board or search vessels may . . . search any trunk or envelope, wherever found, in which he may have a reasonable cause to suspect there is merchandise which was imported contrary to law. . . ."This provision authorizes customs officials to inspect, under Page 431 U. S. 612 the circumstances therein stated, incoming international mail. [Footnote 8]  The "reasonable cause to suspect" test adopted by the statute is, we think, a practical test which imposes a less stringent Page 431 U. S. 613 requirement than that of "probable cause" imposed by the Fourth Amendment as a requirement for the issuance of warrants.  See United States v. King, 517 F.2d 350, 352 Page 431 U. S. 614 (CA5 1975); cf. Terry v. Ohio, 392 U. S. 1,  392 U. S. 8,  392 U. S. 21-22,  392 U. S. 27 (1968).  Inspector Kallnischkies, at the time he opened the letters, knew that they were from Thailand, were bulky, were many times the weight of a normal airmail letter, and "felt like there was something in there."  Under these circumstances, we have no doubt that he had reasonable "cause to suspect" that there was merchandise or contraband in the envelopes. [Footnote 9]  Page 431 U. S. 615 The search, therefore, was plainly authorized by the statute. [Footnote 10]  Since the search in this case was authorized by statute, we are left simply with the question of whether the search, nevertheless violated the Constitution.  Cf. United States v. Brignoni-Ponce, 422 U. S. 873,  422 U. S. 877 (1975).  Specifically, we need not decide whether Congress conceived the statute as a necessary precondition to the validity of the search, or whether it was viewed, instead, as a limitation on otherwise existing authority of the Executive. [Footnote 11]  Having acted pursuant to, and Page 431 U. S. 616 within the scope of, a congressional Act, Inspector Kallnischkies' searches were permissible unless they violated the Constitution.IIIAThat searches made at the border, pursuant to the longstanding right of the sovereign to protect itself by stopping and examining persons and property crossing into this country, are reasonable simply by virtue of the fact that they occur at the border should, by now, require no extended demonstration.  The Congress which proposed the Bill of Rights, including the Fourth Amendment, to the state legislatures on September 2, 1789, 1 Stat. 97, had, some two months prior to that proposal, enacted the first customs statute, Act of July 31, 1789, c. 5, 1 Stat. 29.  Section 24 of this statute granted customs officials "full power and authority" to enter and search "any ship or vessel, in which they shall have reason to suspect any goods, wares or merchandise subject to duty shall be concealed. . . ."  This acknowledgment of plenary customs power was differentiated from the more limited power to enter and search "any particular dwelling-house, store, building, or other place . . ." where a warrant upon "cause to suspect" was required. [Footnote 12]  The historical importance of the Page 431 U. S. 617 enactment of this customs statute by the same Congress which proposed the Fourth Amendment is, we think, manifest.  This Court so concluded almost a century ago.  In Boyd v. United States, 116 U. S. 616,  116 U. S. 623 (1886), this Court observed:"The seizure of stolen goods is authorized by the common law; and the seizure of goods forfeited for a breach of the revenue laws, or concealed to avoid the duties payable on them, has been authorized by English statutes for at least two centuries past; and the like seizures have been authorized by our own revenue acts from the commencement of the government.  The first statute passed by Congress to regulate the collection of duties, the act of July 31, 1789, 1 Stat. 29, 43, contains provisions to this effect.  As this act was passed by the same Congress which proposed for adoption the original amendments to the Constitution, it is clear that the members of that body did not regard searches and seizures of this kind as 'unreasonable,' and they are not embraced within the prohibition of the amendment."(Emphasis supplied.)This interpretation, that border searches were not subject to the warrant provisions of the Fourth Amendment and were "reasonable" within the meaning of that Amendment, has been faithfully adhered to by this Court.  Carroll v. United States, 267 U. S. 132 (1925), after noting that "[t]he Fourth Amendment Page 431 U. S. 618 does not denounce all searches or seizures, but only such as are unreasonable," id. at  267 U. S. 147, recognized the distinction between searches within this country, requiring probable cause, and border searches, id. at  267 U. S. 153-154:"It would be intolerable and unreasonable if a prohibition agent were authorized to stop every automobile on the chance of finding liquor, and thus subject all persons lawfully using the highways to the inconvenience and indignity of such a search.  Travelers may be so stopped in crossing an international boundary because of national self-protection reasonably requiring one entering the country to identify himself as entitled to come in, and his belongings as effects which may be lawfully brought in.  But those lawfully within the country . . . have a right to free passage without interruption or search unless there is known to a competent official authorized to search, probable cause for believing that their vehicles are carrying contraband or illegal merchandise. [Footnote 13]"(Emphasis supplied.)More recently, we noted this longstanding history in United States v. Thirty-seven Photographs, 402 U. S. 363,  402 U. S. 376 (1971):"But a port of entry is not a traveler's home.  His right to be let alone neither prevents the search of his luggage nor the seizure of unprotected, but illegal, materials when his possession of them is discovered during such a search.  Customs officials characteristically inspect luggage, and their power to do so is not questioned in this case; it is an old practice, and is intimately associated with excluding illegal articles from the country. "Page 431 U. S. 619In United States v. 12 200-Ft. Reels of Film, 413 U. S. 123,  413 U. S. 125 (1973), we observed:"Import restrictions and searches of persons or packages at the national borders rest on different considerations and different rules of constitutional law from domestic regulations.  The Constitution gives Congress broad, comprehensive powers '[t]o regulate Commerce with foreign Nations.'  Art. I, § 8, cl. 3.  Historically such broad powers have been necessary to prevent smuggling and to prevent prohibited articles from entry."Finally, citing Carroll and Boyd, this Court stated in Almeida-Sanchez v. United States, 413 U. S. 266,  413 U. S. 272 (1973), that it was "without doubt" that the power to exclude aliens "can be effectuated by routine inspections and searches of individuals or conveyances seeking to cross our borders."  See also id. at  413 U. S. 288 (WHITE, J., dissenting).  Boarder searches, then, from before the adoption of the Fourth Amendment, have been considered to be "reasonable" by the single fact that the person or item in question had entered into our country from outside.  There has never been any additional requirement that the reasonableness of a border search depended on the existence of probable cause.  This longstanding recognition that searches at our borders without probable cause and without a warrant are nonetheless "reasonable" has a history as old as the Fourth Amendment itself. [Footnote 14]  We reaffirm it now.BRespondents urge upon us, however, the position that mailed letters are somehow different, and, whatever may be the normal rule with respect to border searches, different considerations, requiring the full panoply of Fourth Amendment Page 431 U. S. 620 protections, apply to international mail.  The Court of Appeals agreed, and felt that whatever the rule may be with respect to travelers, their baggage, and even mailed packages, it would not "extend" the border search exception to include mailed letter-size envelopes.  176 U.S.App.D.C. at 73, 538 F.2d  at 421.  We do not agree that this inclusion of letters within the border search exception represents any "extension" of that exception.The border search exception is grounded in the recognized right of the sovereign to control, subject to substantive limitations imposed by the Constitution, who and what may enter the country.  It is clear that there is nothing in the rationale behind the border search exception which suggests that the mode of entry will be critical.  It was conceded at oral argument that customs officials could search, without probable cause and without a warrant, envelopes carried by an entering traveler, whether in his luggage or on his person.  Tr. of Oral Arg. 43-44.  Surely no different constitutional standard should apply simply because the envelopes were mailed, not carried.  The critical fact is that the envelopes cross the border and enter this country, not that they are brought in by one mode of transportation rather than another.  It is their entry into this country from without it that makes a resulting search "reasonable."Almost a century ago, this Court rejected such a distinction in construing a protocol to the Treaty of Berne, 19 Stat. 604, which prohibited the importation of letters which might contain dutiable items.  Cotzhausen v. Nazro, 107 U. S. 215 (1883).  Condemning the unsoundness of any distinction between entry by mail and entry by other means, Mr. Justice Miller, on behalf of a unanimous Court, wrote, id. at  107 U. S. 218:"Of what avail would it be that every passenger, citizen and foreigner, without distinction of country or sex, is compelled to sign a declaration before landing, either Page 431 U. S. 621 that his trunks and satchels in hand contain nothing liable to duty, or if they do, to state what it is, and even the person may be subjected to a rigid examination, if the mail is to be left unwatched, and all its sealed contents, even after delivery to the person to whom addressed, are to be exempt from seizure, though laces, jewels, and other dutiable matter of great value may thus be introduced from foreign countries."The historically recognized scope of the border search doctrine, suggests no distinction in constitutional doctrine stemming from the mode of transportation across our borders.  The contrary view of the Court of Appeals and respondents stems, we think, from an erroneous reading of Carroll v. United States, 267 U.S. at  267 U. S. 153, under which the Court of Appeals reasoned that"the rationale of the border search exception . . . is based upon . . . the difficulty of obtaining a warrant when the subject of the search is mobile, as a car or person. . . ."176 U.S.App.D.C. at 70, 538 F.2d  at 418. [Footnote 15]  The fundamental difficulty with this position is that the "border search" exception is not based on the doctrine of "exigent circumstances" at all.  It is a longstanding, historically recognized exception to the Fourth Amendment's general principle that a warrant be obtained, and in this respect is like the similar "search incident to lawful arrest" exception treated in United States v. Robinson, 414 U. S. 218,  414 U. S. 224 (1973).  We think that the language in Carroll v. United States, supra, makes this point abundantly clear.  The Carroll Court Page 431 U. S. 622 quoted verbatim the above-quoted language from Boyd v. United States, 116 U. S. 616 (1886), including the reference to customs searches and seizures of the kind authorized by 1 Stat. 29, 43, as being neither "unreasonable" nor "embraced within the prohibition of the [Fourth] [A]mendment."  Later in the opinion, the Court commented that, having"established that contraband goods concealed and illegally transported in an automobile or other vehicle may be searched for without a warrant, we come now to consider under what circumstances such search may be made."267 U.S. at  267 U. S. 153 (emphasis supplied).  It then, in the passage quoted supra at  431 U. S. 618, distinguished, among these types of searches which required no warrant, those which required probable cause from those which did not:  border searches did not; vehicular searches inside the country did.  Carroll thus recognized that there was no "probable cause" requirement at the border.  This determination simply has nothing to do with "exigent circumstances."The Court of Appeals also relied upon what it described as this Court's refusal in recent years twice"to take an expansive view of the border search exception or the authority of the Boarder Patrol.  See United States v. Brignoni-Ponce, 422 U. S. 873 . . . (1975); Almeida-Sanchez v. United States, 413 U. S. 266 . . . (1973)."176 U.S.App.D.C. at 72, 538 F.2d  at 420.  But, as the language from each of these opinions suggests, 422 U.S. at  422 U. S. 876, 884; 413 U.S. at  413 U. S. 272-273, plenary border search authority was not implicated by our refusal to uphold searches and stops made at places in the interior of the country; the express premise for each holding was that the checkpoint or stop in question was not the border or its "functional equivalent."In view of the wealth of authority establishing the border search as "reasonable" within the Fourth Amendment even though there be neither probable cause nor a warrant, we reject the distinctions made by the Court of Appeals in its opinion. Page 431 U. S. 623Nor do we agree that, under the circumstances presented by this case, First Amendment considerations dictate a full panoply of Fourth Amendment rights prior to the border search of mailed letters.  There is, again, no reason to distinguish between letters mailed into the country and letters carried on the traveler's person. [Footnote 16]  More fundamentally, however, the existing system of border searches has not been shown to invade protected First Amendment rights, [Footnote 17] and hence there is no reason to think that the potential presence of correspondence makes the otherwise constitutionally reasonable search "unreasonable."The statute in question requires that there be "reasonable cause to believe" the customs laws are being violated prior to the opening of envelopes.  Applicable postal regulations flatly prohibit, under all circumstances, the reading of correspondence absent a search warrant, 19 CFR § 145.3 (1976):"No customs officer or employee shall read or authorize or allow any other person to read any correspondence contained in sealed letter mail of foreign origin unless a search warrant has been obtained in advance from an appropriate judge or U.S. magistrate which authorizes such action."Cf. 18 U.S.C. § 1702.We are unable to agree with the Court of Appeals that the opening of international mail in search of customs violations, Page 431 U. S. 624 under the above guidelines, impermissibly chills the exercise of free speech.  Accordingly, we find it unnecessary to consider the constitutional reach of the First Amendment in this area in the absence of the existing statutory and regulatory protection.{18}  Here envelopes are opened at the border only when the customs officers have reason to believe they contain other than correspondence, while the reading of any correspondence inside the envelopes is forbidden.  Any "chill" that might exist under these circumstances may fairly be considered not only "minimal," United States v. Martnez-Fuerte, 428 U. S. 543,  428 U. S. 560,  428 U. S. 562 (1976); cf. United States v. Biswell, 406 U. S. 311,  406 U. S. 316-317 (1972), but also wholly subjective.{19}We therefore conclude that the Fourth Amendment does not interdict the actions taken by Inspector Kallnischkies in Page 431 U. S. 625 opening and searching the eight envelopes.  The judgment of the Court of Appeals is, therefore,Reversed
U.S. Supreme CourtUnited States v. Ramsey, 431 U.S. 606 (1977)United States v. RamseyNo. 76-167Argued March 30, 1977Decided June 6, 1977431 U.S. 606SyllabusTitle 19 U.S.C. § 482 and implementing postal regulations authorize customs officials to inspect incoming international mail when they have a "reasonable cause to suspect" that the mail contains illegally imported merchandise, although the regulations prohibit the reading of correspondence absent a search warrant.  Acting pursuant to the statute and regulations, a customs inspector, based on the facts that certain incoming letter-sized airmail envelopes were from Thailand, a known source of narcotics, and were bulky and much heavier than a normal airmail letter, opened the envelopes for inspection at the General Post Office in New York City, considered a "border" for border search purposes, and ultimately the envelopes were found to contain heroin.  Respondents were subsequently indicted for and convicted of narcotics offenses, the District Court having denied their motion to suppress the heroin.  The Court of Appeals reversed, holding that the border search exception to the Fourth Amendment's warrant requirement applicable to persons, baggage, and mailed packages did not apply to the opening of international mail, and that the Constitution requires that, before such mail is opened, a showing of probable cause must be made and a warrant obtained.Held:1. Under the circumstances, the customs inspector had "reasonable cause to suspect" that there was merchandise or contraband in the envelopes, and therefore the search was plainly authorized by the statute.  Pp.  431 U. S. 611-616.2. The Fourth Amendment does not interdict the actions taken by the inspector in opening and searching the envelopes.  Pp.  431 U. S. 616-625.(a) Boarder searches without probable cause and without a warrant are nonetheless "reasonable" within the meaning of the Fourth Amendment.  Pp.  431 U. S. 616-619.(b) The inclusion of international mail within the border search exception does not represent any "extension" of that exception.  The exception is grounded in the recognized right of the sovereign to control, subject to substantive limitations imposed by the Constitution, who and what may enter the country, and no different constitutional standards should apply simply because the envelopes were mailed, not carried -- the Page 431 U. S. 607 critical fact being that the envelopes cross the border and enter the country, not that they are brought in by one mode of transportation, rather than another.  It is their entry into the country from without it that makes a resulting search "reasonable."  Pp.  431 U. S. 619-621.(c) The border search exception is not based on the doctrine of "exigent circumstances," but is a longstanding, historically recognized exception to the Fourth Amendment's general principle that a warrant be obtained.  Pp.  431 U. S. 621-622.(d) The opening of international mail under the guidelines of the statute only when the customs official has reason to believe the mail contains other than correspondence, while the reading of any correspondence inside the envelopes is forbidden by the regulations, does not impermissibly chill the exercise of free speech under the First Amendment, and any "chill" that might exist under such circumstances is not only "minimal" but is also wholly subjective.  Pp.  431 U. S. 623-624.176 U.S.App.D.C. 67, 538 F.2d 415, reversed.REHNQUIST, J., delivered the opinion of the Court, in which BURGER, C.J., and STEWART, WHITE, POWELL, and BLACKMUN, JJ., joined.  POWELL, J., filed a concurring opinion, post, p.  431 U. S. 625.  STEVENS, J., filed a dissenting opinion, in which BRENNAN and MARSHALL, JJ., joined, post, p.  431 U. S. 625