The nation’s largest group of law professors and a coalition of law schools sued the U.S. Department of Defense and five other federal agencies Friday, claiming a law that forces schools to open their doors to military recruiters is unconstitutional.

The suit marks the first national challenge over the issue to the Defense Department, which last year threatened to cut federal funding to schools, including Yale, that barred military recruiters from interviewing students on campus. The suit centers on the 1995 Solomon Amendment, which requires all colleges and universities that receive federal funding to allow military recruiters access to campus.

Some schools have banned military recruiters because the “don’t ask, don’t tell” policy on homosexuality violates their anti-discrimination policies. The plaintiffs in the lawsuit say the Solomon Amendment threatens the schools’ First Amendment rights.

The Forum for Academic and Institutional Rights, the leading plaintiff in the suit, is keeping anonymous the names of its member law schools to protect federal funding. Yale Law School Dean Anthony Kronman said Yale does not belong to FAIR, though some Yale professors have been involved in planning the lawsuit and may issue declarations to support the plaintiffs.

The group’s board includes professors from Yale, Stanford, Georgetown and New York universities, and the University of Southern California.

Defense Department officials declined to comment on the suit Sunday but have been ordered by the court to respond to the complaint by this Friday.

FAIR President Kent Greenfield, a Boston College law professor, said the Solomon Amendment restricts institutions’ right to free expression.

“They can’t condition whether you get a driver’s license on whether you vote Democratic,” Greenfield said. “Similarly they shouldn’t condition Yale’s medical research funds on whether Yale agrees with the government’s military policy — which is essentially what they’re doing with the Solomon Amendment.”

Faced with the possibility of losing $350 million in federal funds last year, Yale Law School suspended a decades-old nondiscrimination policy and allowed military recruiters to participate in its fall campus interview program. Many other American law schools also made exceptions to their nondiscrimination policies to preserve federal research funding.

In addition to FAIR, the plaintiffs include a coalition of law schools and the Society of American Law Teachers, which includes nearly 900 law professors from over 160 law schools.

While FAIR is not releasing the names of member schools, some universities publicly stated that they were not involved in the lawsuit.

In the hours after the suit was filed, both Harvard and Columbia Universities released statements affirming they were not involved in the suit.

“I did think that it was interesting that a lot of universities went out of their way to say that they weren’t a part of this lawsuit,” Greenfield said. “I think that a lot of universities are scared.”

Federal judge John Lifland, who is hearing the case, denied a request by the plaintiffs to order the government to immediately stop threatening restrictions on federal funding to law schools as a result of the recruiting dispute, The New York Times reported.

–The Associated Press contributed to this report.