"The Constitution is the guardian of our civil rights," said Ralph G. Neas, president of People For the American Way. "Writing discrimination into the Constitution would be a betrayal of our ideals and of the hard-fought progress we have made toward equality for all Americans."

Neas noted that even though Americans are closely divided on the question of same-sex marriages, only a small minority are in favor of enshrining discrimination in the Constitution. A September ABC News poll found that only 20 percent of Americans support amending the Constitution to prohibit same-sex marriage.

"This is a divisive diversionary tactic," said Neas. "There are many urgent issues facing American families as they gather for Thanksgiving this year, but enshrining discrimination in the Constitution is not one of them. Targeting some Americans for second-class citizenship in the Constitution is not a precedent we should even consider setting. Fair-minded Americans should tell their senators to reject this amendment."

The proposed amendment is part of a campaign that was launched by Religious Right groups opposed to equality for gay Americans after the U.S. Supreme Court's Lawrence v. Texas decision. They have intensified their efforts since the Massachusetts Supreme Judicial Court's ruling that the state constitution prohibits the state from denying the rights and responsibilities of civil marriage to same-sex couples. The same amendment was introduced in the House of Representatives earlier this year.