The USA is a union and colonized the Philippines involuntarily. Many Filipinos at the time of independence, wanted our country to remain as a colony of the USA. Also a lot of modern Filipinos voluntarily desire to be a colony of the USA. I should know because I am one of them and I have two cousins that also want the Philippines to be an American colony.
It has been alleged that the Russian Federation colonized Crimea involuntarily. The Soviet Union was criticized as the "Soviet Empire". Jan Zielonka in his book, "Europe as Empire: The Nature of the Enlarged European Union" criticized the EU for having traits characteristic of an empire. The lines between empires and federations are blurring.