"Terms of Union" exist between the federal government of Canada and three Canadian provinces: British Columbia (1871), Prince Edward Island (1873), and Newfoundland and Labrador (1949). These documents once paved the way for three provinces to join Confederation. But they have also since been amended several times, and occasionally become sites of political controversy. While it is not clear that these documents are “treaties”, they do impose unique legal, constitutional and political obligations and rights on the signatory governments – obligations and rights which may not exist for other provinces. The function of these Terms of Union agreements is described and analyzed by comparing the case studies of the British Columbia railway dispute in the late 19th century and denominational education reforms in 1990s Newfoundland and Labrador. These events show not only that Terms of Union remain relevant in any discussion of constitution politics in the provinces where they exist, they are also sources of asymmetical federalism.