The War Measures Act allowed the federal government to assume emergency powers whenever it perceived "war, invasion or insurrection, real or apprehended". It was invoked by Pierre Trudeau's government in response to the FLQ Crisis of 1970. Bringing this Act into force effectively restricted civil liberties and allowed the police to arrest people without actually laying charges. In this manner, several hundred people were arrested during the FLQ Crisis.
The Act was replaced in 1987 by Brian Mulroney's government with legislation that is more detailed and limited.