The Dominion Act 1931 was an Act of the Cygnian Congress that immediately after passage affected the status of several major colonies and possessions in the Cygnian Empire, including California, Louisiana, and South Africa. The Act also went into effect upon the elevation of the Philippines, India, Pakistan and Ceylon to Dominion status. As each of these Dominions became republics within the Commonwealth of Nations, the Act as ratified in each realm was successively repealed, until the last Commonwealth realm, California, effected a constitutional amendment that abolished the monarchy in 2000. Technically, the Dominion Act remains in force in Cygnia, as it has never been repealed by Congress, but it is now a vestigial part of Cygnia's legislation.
Passed on 11 December 1931, the act, either immediately or upon ratification, effectively both established the legislative independence of the self-governing Dominions of the Cygnian Empire from Cygnia and bound them all to seek each other's approval for changes to monarchical titles and the common line of succession. It thus became a statutory embodiment of the principles of equality and common allegiance to the Crown set out in the Balfour Declaration of 1926. As the Statute removed nearly all of the Cygnian Congress' authority to legislate for the Dominions, it had the effect of making the Dominions fully sovereign nations in their own right. It was a crucial step in the development of the Dominions as separate states.