WASHINGTON, D.C., JUNE 27, 2004 (Zenit.org).- The president of the U.S. bishops' conference is exhorting prelates to personally urge their senators to support a constitutional amendment defining marriage as exclusively between one man and one woman.

The first vote on the proposed amendment to the U.S. Constitution may occur in the Senate as early as mid-July.

The proposal, popularly known as the Federal Marriage Amendment, reads as follows: "Marriage in the United States shall consist only of the union of a man and a woman. Neither this Constitution, nor the constitution of any State, shall be construed to require that marriage or the legal incidents thereof be conferred upon any union other than the union of a man and a woman."

In a letter to his fellow U.S. prelates, Bishop Wilton Gregory, president of the episcopate, noted that the proposed amendment leaves legislative decisions on civil unions or domestic partnerships up to the state legislatures.

Opponents of the Federal Marriage Amendment are expected to mount a filibuster against the proposed amendment, so the key vote in the Senate will likely occur on a motion to bring debate to a close.

Such an end to debate is necessary before the Senate can vote on the substance of the Federal Marriage Amendment, Bishop Gregory said. "Your message should also strongly support any effort to stop a 'filibuster' and allow the Senate to vote on this vitally important matter," he wrote in the letter dated last Thursday.

In his letter to the bishops, Bishop Gregory recalled that the U.S. bishops' conference has been working on the marriage issue for many years, supporting state efforts to preserve marriage as a union of a man and a woman.

"As the U.S. Bishops have previously written, marriage is a basic human and social institution," Bishop Gregory said. "Though it is regulated by civil laws and church laws, it did not originate from either the church or state, but from God. Therefore neither church nor state can alter the basic meaning and structure of marriage."

"However, a growing movement today favors making those relationships commonly called same-sex unions the legal equivalent of marriage," he continued. "This situation challenges Catholics -- and all who seek the truth -- to think deeply about the meaning of marriage, its purposes, and its value to individuals, families and society."