Swiss voters will get final say on whether same-sex couples can marry after opponents gathered enough signatures to force a binding referendum on a 2020 law allowing them to wed. That legislation also allowed transgender people to change their legal gender with a declaration, in a major change for a country that has lagged other parts of western Europe in gay rights. The Swiss government certified that opponents had gathered enough support to call a referendum under the nation’s system of direct democracy. It will in May set a date for the vote, which could come in September at the earliest, a spokesman said. Opponents had decried “fake marriages” and said only a man and a woman could wed.