Selective enforcement

In law, selective enforcement occurs when government officials such as police officers, prosecutors, or regulators exercise enforcement discretion, which is the power to choose whether or how to punish a person who has violated the law. The biased use of enforcement discretion, such as that based on racial prejudice or corruption, is usually considered a legal abuse and a threat to the rule of law.
In some cases, selective enforcement may be desirable. For example, a verbal warning to a teenager may effectively alter their behavior without resorting to legal punishment and with the added benefit of reducing governmental legal costs. In other cases, selective enforcement may be inevitable. For example, it may be impractical for police officers to issue traffic tickets to every driver they observe exceeding the speed limit, so they may have no choice but to limit action to the most flagrant examples of reckless driving.
Immigration law.
More recently this has become a topic of great discussion in the illegal immigration debate in the United States. The 2011 "Morton Memo" laid out enforcement priorities for the U.S. Immigration and Customs Enforcement, and was intended to channel limited resources into prioritized pursuit of cases involving criminals and felons. It was interpreted as the waiver of active prosecution of non-criminal illegal aliens and the exclusive focus on criminal illegal aliens. Enforcement priorities were further defined by the Deferred Action for Childhood Arrivals program, which started in 2012. This uses the executive branch's discretionary authority to grant certain people who were illegally brought to the United States as minors the temporary authorization to live and work in the United States.
By country.
United States.
In the United States federal system, the prosecutor has wide latitude in determining when, who, how, and even whether to prosecute for apparent violations of federal criminal law. The prosecutor's broad discretion in such areas as initiating or forgoing prosecutions, selecting or recommending specific charges, and terminating prosecutions by accepting guilty pleas has been recognized on numerous occasions by the courts.
Wayte v. United States 470 U.S. 598 (1985) said:In our criminal justice system, the Government retains "broad discretion" as to whom to prosecute. [...] This broad discretion rests largely on the recognition that the decision to prosecute is particularly ill-suited to judicial review. Such factors as the strength of the case, the prosecution's general deterrence value, the Government's enforcement priorities, and the case's relationship to the Government's overall enforcement plan are not readily susceptible to the kind of analysis the courts are competent to undertake."Yick Wo v. Hopkins" (1886) was the first case where the United States Supreme Court ruled that a law that is race-neutral on its face, but is administered in a prejudicial manner, is an infringement of the Equal Protection Clause in the Fourteenth Amendment to the U.S. Constitution.