Alberta has never successfully invoked the notwithstanding clause, but in March 2000, the Legislature of Alberta passed Bill 202, which amended the province's Marriage Act to include an opposite-sex-only definition of marriage as well as the notwithstanding clause in order to insulate the definition from 'Charter challenges. However, a legislature may only use the "notwithstanding clause" on legislation it would otherwise have the authority to enact, and the Supreme Court of Canada ruled in "Reference re Same-Sex Marriage" that the definition of marriage is within the exclusive domain of the Parliament of Canada, thus finding the legislation "ultra vires", or beyond the constitutional powers of the Alberta Legislature.