Five people in Japan are poised to launch an unprecedented lawsuit against the government, claiming that a civil law forcing them to choose a single surname after marriage violates their constitutional rights. If they succeed, married men and women will for the first time be able to retain their own surnames, dealing a blow to one of the few remaining legal obstacles to gender equality. In the vast majority of cases, women are required to relinquish their maiden name after marriage, although a small number of men take their wife's name.