U.S. Senate Majority Leader Bill Frist says floor debate will begin a week from Monday on a proposed constitutional amendment defining marriage as the union of a man and a woman.

He said the amendment is needed to stop judges from ordering the legalization of same-sex marriage despite the opposition of voters and their elected representatives.

Frist and three other senators were joined at a news conference by representatives of some black and Hispanic churches and the U.S. Conference of Catholic Bishops.

Knoxville Bishop Joseph Kurtz said neither the church nor the state has the right to redefine marriage, because it comes from God.

Supporters of the amendment believe they have a Senate majority, if not the two-thirds needed to amend the Constitution.

Amending the Constitution requires two-thirds approval by both the Senate and the House of Representatives, as well as ratification by three-fourths of the states.

Over the last few years, at least 19 states have approved constitutional definitions of marriage to prevent same-sex couples from getting married.