Ultra vires is a Latin phrase used in law to describe an act that requires legal authority but is done without it. Its opposite, an act done under proper authority, is intra vires. Acts that are intra vires may equivalently be termed "valid", and those that are ultra vires termed "invalid".
Legal issues relating to ultra vires can arise in a variety of contexts:
Judicial discretion is the power of the judiciary to make some legal decisions according to their discretion. Under the doctrine of the separation of powers, the ability of judges to exercise discretion is an aspect of judicial independence. Where appropriate, judicial discretion allows a judge to decide a legal case or matter within a range of possible decisions.
However, where the exercise of discretion goes beyond constraints set down by legislation, by binding precedent, or by a constitution, the court may be abusing its discretion and undermining the rule of law. In that case, the decision of the court may be ultra vires, and may sometimes be characterized as judicial activism.
A designated activity company (Irish: Cuideachta Ghníomhaíochta Ainmnithe) or DAC is a form of company in Ireland created by the Companies Act 2014. Like a limited company, designated activity companies have limited liability. Additionally, they may only carry out activities listed in their constitution documents, and so the concept of ultra vires continues to apply to them. Notable DACs include Ryanair and Ulster Bank.