BUCHAREST — Romania set an Oct. 6-7 date for a referendum to change the constitutional definition of marriage to a union between a man and a woman, aimed at preventing same sex partnerships from ever being legal in one of the few EU states to still ban them.

Most EU countries allow either same-sex marriages or civil partnerships, but Romania does not even recognize those performed abroad. Its constitution now defines a family as including spouses, without explicitly specifying their sex.

A group called Coalition for the Family has collected 3 million signatures in favor of the change. The lower house of parliament voted in favor last year and the senate voted earlier this month, making the referendum the last stage needed to enact the change.

Few politicians openly support same sex marriage or civil partnerships in the socially conservative eastern European nation of 20 million, where the Orthodox Church wields significant influence.

For any referendum to be valid, a third of more than 18 million Romanians with voting rights must turn out to the polls.

Rights groups are urging people to boycott the ballot, saying human rights should not be put up for a vote. They say restricting the definition of family to one based on a marriage between a man and a woman would also hurt single parents, non-married couples and other non-traditional parenting units, as well as same-sex couples.

Under Romanian law, the constitution can be changed after a proposal by the president, the government, a quarter of all lawmakers or at least 500,000 citizens. Parliament must approve any revision, which must then pass a nationwide referendum.

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