A demonstrator waves a rainbow flag in front of the US Capitol in Washington on October 11, 2009 as tens of thousands of gay activists marched to demand civil rights, a day after President Barack Obama vowed to repeal a ban on gays serving openly in the US military.

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Bernie Sanders, Nancy Pelosi and Cory Booker among the lawmakers who signed the brief

Lawsuit is from an openly gay man who said one of his supervisors created a "pervasive hostile workplace atmosphere"

Washington CNN  — 

Addressing what could be the next frontier in gay rights litigation, 128 Democratic members of Congress filed a brief in federal court on Wednesday arguing that a civil rights law should be interpreted to include claims of discrimination based on sexual orientation.

The friend-of-the-court brief was submitted in support of Matthew Christiansen, an openly gay man who is HIV positive, who is suing his employer under Title VII of the Civil Rights Act of 1964 that prohibits employers from discriminating against employees on the basis of sex.

Democratic presidential candidate Sen. Bernie Sanders, House Minority Leader Nancy Pelosi, and Sens. Cory Booker, Al Franken, Tim Kaine and Patrick Leahy are among the signatories.

Christiansen filed suit against his employer, Omnicom Group, alleging that one of his supervisors created a “pervasive hostile workplace atmosphere” in part by drawing sexually explicit pictures among other acts.

“At the heart of this appeal is whether Title VII protects those males and females whose sexual orientation is not heterosexual,” Susan Chana Lask, Christiansen’s lawyer, argued in court papers.

This is the first time members of Congress have weighed in on this issue in federal court, said Peter T. Barbur, the lawyer representing the lawmakers.

“To hold that sexual orientation does not fall under ‘sex’ in Title VII flies in the face of common sense,” Barbur wrote. The signers of the brief are also cosponsors of the Equality Act, a legislative effort aimed at updating the nation’s laws with respect to LGBT Americans.

Christiansen lost at the district court level when the judge ruled that as the law currently stands in her jurisdiction his claim could not be brought under Title VII.

If Christiansen were to win his appeal, it would set an important precedent for future cases involving gay, lesbian and bisexual employees who face discrimination by their employers. There are about 28 states that do not provide express protection against discrimination based on sexual orientation. Supporters of Christiansen say that Title VII would be the only remedy for LGBT workers in those states.

Lawyers for Omnicom Group rejected several of Christiansen’s claims including the one targeting Title VII. “This claim is based on allegations of sexual orientation discrimination which is not legally cognizable under Title VII” they wrote in court papers.

The U.S. Equal Employment Opportunity Commission has also filed a brief in the case in support of Christiansen’s claim. In court papers EEOC lawyers argue that claims of sexual orientation can be made under Title VII because they involve sex stereotyping, gender-based associational discrimination, and consideration of an individual’s sex.” They also point to recent Supreme Court decisions and say the “legal landscape has changed.”

No federal appeals court has recognized that Title VII prohibits discrimination based on sexual orientation.

“The EEOC was absolutely correct in concluding last year that sexual orientation discrimination, is a form of sex discrimination, and we hope that the 2nd circuit and other federal courts will agree,” said Chris Stoll of the National Center for Lesbian Rights who is also filed a brief in the case.

Arthur Leonard, a professor at New York Law School, says that though some federal district courts have ruled that such claims can be made, an appeals court ruling would make a big impact.

“A federal appeals court ruling allowing such claims would be a major breakthrough,” Leonard said, “and could lead to a Supreme Court decision that would effectively ban sexual orientation discrimination in employment nationwide.”

James Esseks, the director of the ACLU’s LGBT Project said his group is working with Congress to get “explicit” protections enacted into law.

“As that work continues, we must ensure that courts are correctly interpreting federal civil rights laws in a way that robustly protects the rights of LGBT people across the U.S,” he said.