Originally courts granted only prohibitory injunctions, on the grounds that the performance of affirmative orders could not be easily compelled or supervised. In the 19th cent., though, affirmative (mandatory) injunctions began to be used, and they are now granted in unusual circumstances. Injunctions issued while an action is pending are termed preliminary, or interlocutory; they are intended to protect the plaintiff's interest so that a final judgment will not be worthless, and they cannot, for the most part, be reviewed by higher courts. If irreparable injury would result even before notice of a hearing could be served, the court may grant a temporary restraining order, which is binding on the defendant until a hearing can be held. A final or perpetual injunction is part of the final judgment of the court, and may be issued after all the evidence has been heard.
Injunctions, like most remedies of an equitable nature, are usually granted by a judge sitting without a jury. The broad discretion courts have enjoyed in using this power has, however, been limited by statute in many areas of the law. An injunction is essentially a personal order, and a defendant who disobeys may be punished for contempt. An injunction in force may be terminated or modified by the court.
Injunctions are today granted in many circumstances where courts of equity formerly refused to act. Thus, courts have ordered the performance of the terms of a contract, or the payment of legal damages by a defendant, sparing the plaintiff the need to seek execution of a judgment. Injunctions have long been used to abate nuisances. The use of the injunction in labor disputes has been a matter of great controversy in U.S. history.
In the late 19th cent. employers were often granted injunctions against strikes or boycotts when they alleged that the purpose of labor's activity (e.g., unreasonably limiting the employer's freedom by requiring him to hire only union members) was illegal. The power of federal courts to enjoin union activity was restricted by the Federal Anti-Injunction (Norris-LaGuardia) Act of 1932, and many states passed similar laws. Later legislation, however, including the 1947 Taft-Hartley Labor Act and the 1959 Labor Management Reporting and Disclosure Act, restored much of the power to use labor injunctions.
A temporary restraining order may be granted ex parte, that is, without informing in advance the party to whom the temporary restraining order is directed. Usually, a party moves ex parte to prevent an adversary from having notice of one's intentions. The order is granted to prevent the adversary from acting to frustrate the purpose of the action, for example, by wasting or hiding assets (as often occurs in dissolution of marriage) or disclosing a trade secret that had been the subject of a non-disclosure agreement.
Many states have injunction laws that are written specifically to stop domestic violence, stalking, sexual assault or harassment and these are commonly called restraining orders, orders of protection, or protective orders.
Unable to limit what they called "government by injunction" in the courts, labor and its allies persuaded the U.S. Congress in 1932 to pass the Norris-LaGuardia Act, which imposed so many procedural and substantive limits on the federal courts' power to issue injunctions as to effectively prohibit all federal court injunctions in cases arising out of labor disputes. A number of states followed suit and enacted "Little Norris-LaGuardia Acts" that imposed similar limitations on state courts' powers. The courts have since recognized a limited exception to the Norris-LaGuardia Act's strict limitations in those cases in which a party seeks injunctive relief to enforce the grievance arbitration provisions of a collective bargaining agreement.