Croatian voters have approved an amendment to their country's constitution that defines marriage as the union of a man and a woman.

Cardinal Josip Bozanic encouraged a "yes" vote, noting in a letter read to parishioners that marriage is "the only union enabling procreation."

The Dec. 1 referendum passed by nearly a 2-to-1 margin, with about 65 percent of Croatians voting in favor and about 34 percent voting against it, the Associated Press reports.

Referendum supporters, including the group In the Name of the Family, gathered 750,000 signatures in the predominantly Catholic country to place the measure on the ballot.

Supporters of the referendum cited concerns among many Croatians that the government would try to redefine marriage to include same-sex unions. Croatia's President Ivo Josipovic and Prime Minister Zoran Milanovic both opposed the referendum.

Government leaders are backing a bill allowing same-sex couples to register as "life partners" and secure some legal rights. A 2003 law recognizes same-sex unions for couples who have lived together for at least three years.

The Dec. 1 vote was the first citizen-launched referendum since Croatia became independent from the former Yugoslavia in 1991.

Zeljka Markic, a backer of the initiative, welcomed its success.

"We showed that we know, like David fighting against Goliath, how to direct our small slingstones in the same direction," she said, according to the Sydney Morning Herald. "This time for the protection of marriage, and next time for something else of the same importance."