What is the theory of ultra vires in administrative law?

The theory of ultra vires in administrative law refers to actions taken by public authorities or agencies that exceed the powers granted to them by law. When an authority acts ultra vires, its actions are considered invalid and unenforceable. This principle ensures that public bodies operate within the legal frameworks established by legislation, safeguarding against arbitrary or unlawful decision-making. It serves as a vital mechanism for upholding the rule of law and protecting individual rights against misuse of power.