OLYMPIA, Wash. - An initiative filed by proponents of same-sex marriage would require heterosexual couples to have kids within three years or else have their marriage annulled.

Initiative 957 was filed by the Washington Defense of Marriage Alliance. That group was formed last summer after the state Supreme Court upheld Washington's ban on same-sex marriage.

Under the initiative, marriage would be limited to men and women who are able to have children. Couples would be required to prove they can have children in order to get a marriage license, and if they did not have children within three years, their marriage would be subject to annulment.

All other marriages would be defined as "unrecognized" and people in those marriages would be ineligible to receive any marriage benefits.

“For many years, social conservatives have claimed that marriage exists solely for the purpose of procreation ... The time has come for these conservatives to be dosed with their own medicine," said WA-DOMA organizer Gregory Gadow in a printed statement. “If same-sex couples should be barred from marriage because they can not have children together, it follows that all couples who cannot or will not have children together should equally be barred from marriage."

Supporters must gather more than 224,000 valid signatures by July 6 to put the initiative on the November ballot.

Opponents say the measure is another attack on traditional marriage, but supporters say the move is needed to have a discussion on the high court ruling.