Under Japanese law, it is illegal to have multiple wives at the same time, but polygamy was once common among aristocrats and samurai during medieval times in Japan. Modern-day polygamy is rare in Japan, but there are some cases where men may have mistresses or engage in extramarital affairs without their wives' knowledge or consent. Anyone who violates the law can face imprisonment for up to three years or a fine of up to 500,000 yen ($4,600). Some religious groups practice polygamy in Japan, and due to strict immigration laws, some men may resort to fake marriages with foreign women to gain residency in the country. The declining marriage rate and changing attitudes towards marriage suggest that traditional norms are shifting in Japan.