A federal subpoena is a formal request for information or property issued by a federal court judge. A subpoena is a legal order that commands the person requested to either appear, turn over information, or surrender property to a law enforcement official. A subpoena is appropriate to compel a witness to testify in the event of a crime or to compel someone to turn over evidence or property.
The most common reason for a subpoena is when a witness to a crime, or to an incident giving rise to a legal cause of action, does not wish to testify. The person is referred to as a hostile witness because he may have the necessary information a plaintiff, prosecutor or defendant needs to prove his case, but he may be unwilling to turn over that information for some reason. As such, a subpoena can compel him to come to court to share what he knows or to turn over the evidence desired. Because the justice system depends on the court, judge and jury receiving as much information as possible to decide a case, the court has the right to issue the subpoena to compel testimony in the interest of justice.
A federal subpoena is issued by a judge within the federal court system. This system is a court of more limited jurisdiction than a state court system. The federal court can hear cases only when a federal issue or question is at stake or when diversity jurisdiction exists. Federal issues or questions mean that the parties are having a dispute in which federal law governs or that the issue is one arising from the Constitution. Diversity jurisdiction exists when two parties from different states or when a citizen and an alien are having a dispute over $10,000 US Dollars (USD) or more.
Therefore, a federal subpoena will only be issued by a federal judge in cases being heard in federal court. One or the other party — either the plaintiff, prosecutor or defendant — will make a request that the judge issue the subpoena to help him collect the evidence he needs to make his case. The judge will review the request for the federal subpoena and issue it or deny it. The federal subpoena will then be delivered to the person being subpoenaed and he will either have to comply with the request made in the subpoena or he will be held in contempt of federal court and possibly subject to jail time.