Opposition proceeding

An opposition proceeding is an administrative process available under the patent and trademark law of many jurisdictions which allows third parties to formally challenge the validity of a pending patent application ("pre-grant opposition"), of a granted patent ("post-grant opposition"), or of a trademark.
Patents.
European Patent Organisation.
In the context of the proceedings at the European Patent Office (EPO), third parties may dispute the validity of a granted European patent by filing a post-grant opposition under the European Patent Convention (EPC). The term for filing an opposition with the EPO is nine months from the publication of the mention of the grant of the European patent in the European Patent Bulletin.
France.
As of April 1, 2020, opposition proceedings will also be available in France. The term for filing an opposition with the National Institute of Industrial Property (INPI) will be nine months from the grant of the French patent.
United States.
Under United States patent law, an opposition proceeding is called a reexamination. Post-grant review provisions of the new patent law may affect a potential patent infringement defendant's strategies in filing a declaratory judgment action. Subsequent to the Leahy–Smith America Invents Act (2011), any third party can challenge the validity of an issued patent using either post-grant review under 35 U.S.C. § 321 or inter partes review under 35 U.S.C. § 311. Both proceedings became effective September 16, 2012.
Trademarks.
In the case of trademarks, third parties may use opposition proceedings to "oppose" the acceptance of a trademark application after it has been accepted and published for opposition purposes. If an opposition is defeated the trademark will proceed to registration. Some jurisdictions operate a "post-grant" opposition system, whereby opposition is not possible until after registration (e.g. Japan).
Canada.
In Canada, any third party can file a statement of opposition to stop a trademark from being registered for at least one of the reasons set out in the "Trademarks Act" and "Trademarks Regulations". A statement of opposition can only be filed during the two-month period after a trademark application is approved by the Canadian Intellectual Property Office (CIPO) and advertised in the "Trademarks Journal". The trademark applicant and opponent then submit pleadings, evidence and arguments to the Trademarks Opposition Board (an administrative body within CIPO), which hears and makes decisions in opposition proceedings. The Board can either refuse the trademark application (in whole or in part) or reject the opposition. This decision can be appealed to the Federal Court of Canada by both the trademark applicant and opponent.