In the United States federal court system, the issuance of writs is authorized by U.S. Code, Title 28, Section 1651. The language of the statute was left deliberately vague in order to allow the courts flexibility in determining what writs are necessary "in aid of their jurisdiction". Use of writs at the trial court level has been greatly curtailed by the adoption of the Federal Rules of Civil Procedure and its state court counterparts, which specify that there is "one form of action".