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Exactly one month after a lone gunman massacred 49 people at a gay club in Orlando, House lawmakers held a hearing on a bill that critics believe will open the door to LGBT discrimination.

At the hearing Tuesday, Democratic lawmakers and one of their chosen witnesses made sure to underscore that fact.

"This hearing is deeply hurtful to a still grieving LGBT and allied community," former Supreme Court plaintiff Jim Obergefell told the Republicans on the House Committee on Oversight and Government Reform on Tuesday.

Related: Same-Sex Marriage Proposed, Rejected for GOP Platform

The measure, known as the First Amendment Defense Act (FADA), would bar the federal government from taking “any discriminatory action against a person, wholly or partially on the basis that such person believes or acts in accordance with a religious belief or moral conviction that marriage is or should be recognized as the union of one man and one woman, or that sexual relations are properly reserved to such a marriage.”

Originally introduced last year by Rep. Raul Labrador, the measure currently has 171 co-sponsors — all Republican except for one, Democratic Rep. Daniel Lipinski of Illinois.

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Supporters insist the bill is necessary to protect "religious liberty" since marriage is legal nationwide for same-sex couples.

"It has never been our intention to give anyone a so-called license to discriminate," Labrador testified. "Our bill does not take away anybody’s rights. It just attempts to enshrine in law religious liberties long believed to be protected."

Rep. Raul Labrador, (R-ID), center, speaks while flanked by Sen. Mike Lee, (R-UT), left, and former Rep. Barney Frank, (D-MA), during a House Oversight and Government Reform Committee hearing on July 12. The committee heard testimony regarding the First Amendment Defense Act, which opponents fear will weaken existing protections for LGBT people. Mark Wilson / Getty Images

But opponents fear it will weaken existing protections for LGBT people — including an executive order banning federal contractors from discriminating on the basis of sexual orientation or gender identity, and a requirement that hospitals receiving Medicare and Medicaid allow patients to have any visitors they choose, including same-sex spouses.

The broad language of the bill, including protection for those who believe “sexual relations are properly reserved to” marriage, suggests it could also be applied in cases of unmarried heterosexual couples.

"Is it conceivable that a single woman with a child could be denied housing?" Rep. Bonnie Watson Coleman, Democrat from New Jersey, asked one of the other Democrats' witnesses, Columbia Law School Professor Katherine Franke.

Related: One year after marriage ruling, fight for equality continues

"That could happen every day," Franke replied. But, she added, "The landlord would have a defense under FADA." Franke said the bill was "creating a solution to a problem that does not exist" and that it raised its own First Amendment questions by "upsetting the delicate balance" between individual beliefs and the federal government enabling the imposition of those beliefs on others.

Former congressman Barney Frank also testified against the bill. When his former colleague Rep. Mick Mulvaney, a Republican, asked about the fears among same-sex marriage opponents that their tax exemptions would soon be at risk, Frank retorted, "There are some people who think Elvis is alive." He drew a distinction between a federal grant, which he said requires more scrutiny and compliance with anti-discrimination precepts, and a tax exemption.

Kelvin Cochran, the Atlanta fire chief who was fired amid a controversy over writing a book describing homosexuality as “vile, vulgar and inappropriate,” testified in favor of the bill. FADA would not have protected Cochran, who was a city employee. But even some of the bill's opponents, including Frank, expressed uneasiness at Cochran's 2015 firing, arguing the book fell outside the scope of his employment.

Whether FADA passes constitutional muster remains to be seen; the bill bears striking resemblance to a law in Mississippi that was recently struck down by a federal judge.