An exception was made to the section 50 rule in 1916 so that the House of Commons in the 12th Canadian Parliament could last longer than five years due to the First World War, but this was through a one-time constitutional amendment (the British North America Act, 1916). The British North America (No. 2) Act, 1949 amended the division of powers in the Constitution Act, 1867, by adding section 91(1). This limited which portions of the constitution that the Parliament of Canada could unilaterally amend. One rule that Parliament could not unilaterally amend was that the House of Commons could not last for more than five years without an election, unless war or rebellion caused two-thirds or more of the House to believe a longer term would be necessary. It read,
