The National Organization for Marriage (NOM) on Friday called on the U.S. Senate to reject the Employment Non-Discrimination Act (ENDA).

ENDA, which was first proposed in 1994, seeks workplace protections based on sexual orientation and gender identity. The measure cleared a Senate committee with the help of three Republicans in July and a full floor vote is expected on Monday.

(Related: Senate vote on gay protections bill ENDA set for Monday.)

But NOM warned in a blog post that the bill “is nothing other than a Trojan horse built to attack the foundational institution of marriage between a man and a woman.”

“This disastrous piece of legislation is modeled on various local and state non-discrimination statutes that have already been used as tools in advancing the same-sex 'marriage' agenda around the nation,” NOM President Brian Brown wrote on his group's website. “In the wake of Justice Kennedy's misguided opinion in the DOMA case (Windsor v. U.S.), it is certain that this federal ENDA bill will become a fulcrum used by same-sex 'marriage' activists to try to foist a marriage redefinition regime on the entire country.”

Brown incorrectly stated: “Under the law, individuals holding the common-sense belief that marriage is about giving kids a mom and a dad would be subject to punishment. Expressions of support for true marriage in the workplace would no longer be a fundamental right, but discriminatory, bigoted and an actionable offense!”

Brown called on members to contact 8 Republican senators, including John McCain of Arizona, Rob Portman of Ohio, Orrin Hatch of Utah, Kelly Ayotte of New Hampshire, Jeff Flake of Arizona, Dean Heller of Nevada, Pat Toomey of Pennsylvania and John Barrasso of Wyoming.

A sample voicemail instructs callers to tell the senators that ENDA “will put [marriage equality opponents] in even more danger of being labeled bigots or haters by those who disagree with them.”

(Related: NOM's Brian Brown: Federal marriage amendment needed to reign in judges.)