WASHINGTON (AP) — Senate Democrats are intent on keeping out a provision from the annual defense policy bill that they say would undercut protections against workplace discrimination based on sexual or gender orientation.

In a letter delivered Tuesday, the lawmakers called the provision dangerous. They said the measure would permit religiously affiliated federal contractors to refuse to interview a job candidate whose faith differs from theirs and to fire employees that marry their same-sex partners or use birth control. But Republican proponents of the measure have described the provision as a bulwark for religious freedom.

The House added the provision to its version of the defense policy bill. The Senate did not, leading to a standoff. The divide could threaten the timely approval of the defense legislation, which authorizes military programs for the new fiscal year that started Oct. 1.

Congress returns after the Nov. 8 election for a lame-duck session and will be under pressure to resolve differences between the two chambers and get a final bill to the president's desk.

Forty lawmakers, joined by two independents, signed the letter to Sen. John McCain, R-Ariz., and Rep. Mac Thornberry, R-Texas, the chairmen of the Armed Services panels. The committee's top Democrats, Sen. Jack Reed of Rhode Island and Adam Smith of Washington state, also received the letter. But Republicans control deliberations over the bill, known formally as the National Defense Authorization Act.

They said the provision is at odds "with the values and beliefs that continue to advance our great nation," yet there is no overt threat in the letter to block the defense authorization bill if the measure is added.

"This discrimination erodes the freedoms that our military has fought for generations to protect," the lawmakers wrote.

The provision would "vastly expand religious exemptions" under the Civil Rights Act and Americans with Disabilities Act to allow contractors "to harm hardworking Americans who deserve to be protected from workplace discrimination based on sexual orientation, gender identity, religious identity, or reproductive and other healthcare decisions," according to the letter.

The House provision was authored by Rep. Steve Russell, R-Okla., who said the provision is aimed at ensuring faith-based organizations that perform work for the U.S. government aren't forced to act against their beliefs.