A major lawsuit filed by multiple national fraternities and sororities has accused Harvard University of discouraging students from joining single-gender social groups.

The lawsuit, filed Monday in Boston’s federal court, marked the first legal challenge to the school’s policy that was implemented in 2016.

Two fraternities and two sororities joined the lawsuit, while another sorority separately sued the school in Massachusetts state court. Both cases argue that the school's policy discriminates against students based on their sex and spreads negative stereotypes about students who join all-male or all-female organisations.

“The common thread that ties together all of Harvard's ever-shifting justifications for the sanctions policy is sexism,” the suit says. “Harvard's views that all-male organisations cause sexual assault because they are all-male, and that there is no value to all-female or all-male organisations, are sexist in the extreme.”

Also suing Harvard in the federal case are two anonymous male students who say they have been unfairly denied campus leadership roles because of the rule, and another who is not subject to the policy because he's an upperclassmen but says he has faced negative stigma created by the rule.

Harvard officials did not immediately respond to The Independent's requests for comment on the suits.

The university’s policy prohibits Harvard students who are members of single-gender groups from leading campus clubs or becoming captains of sports teams, beginning with last year’s freshman class.

The school crafted the rule as part of an effort to curb secretive all-male groups known as “final clubs” — some of which have included former US presidents and other high-profile alumni.

Harvard also refuses to endorse those students for prestigious fellowships, including the Rhodes and Marshall scholarships.

The policy arose from a 2016 report accusing single-sex organisations at Harvard of possessing “deeply misogynistic attitudes” and linking those sentiments to sexual assaults that took place at the university.

But the rule also applies to a variety of other groups, including fraternities, sororities and even single-gender musical groups. Since the rule took effect last year, at least three sororities have cut ties with their national organisations and reopened as groups open to members of any sex.

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Harvard does not officially recognise any fraternities or sororities, but several have been available to Harvard students in the past, often with houses located near campus in Cambridge, Massachusetts.

The sororities suing Harvard in federal court are Kappa Alpha Theta and Kappa Kappa Gamma, whose local chapters disbanded and said they would become co-ed groups.

The two fraternities in the federal suit, Sigma Chi and Sigma Alpha Epsilon, say they have struggled to recruit students and have faced financial difficulty with fewer dues-paying members.

The federal suit says Harvard's rule violates the 1972 law known as Title IX, which forbids discrimination based on sex in schools that receive federal funding. It also says Harvard's policy singles out women and men for punishment because of their sex, and relies on stereotypes about men and women.

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The lawsuit filed in state court similarly argues that the rule violates civil rights laws in Massachusetts. That case was filed by the Alpha Phi sorority and its Harvard chapter, along with the Delta Gamma Fraternity Management Corporation, an Ohio-based group that supports the Delta Gamma sorority, whose local chapter shut down in August.

Both suits demand a jury trial and ask the courts to stop Harvard from enforcing the policy.