The LGBT legal group GLAD has filed a class action lawsuit against Walmart, charging the retail giant with discriminating against gay workers.

The lawsuit, Jacqueline Cote, et al. v. Wal-Mart Stores, Inc., alleges that Walmart violated Title VII of the federal Civil Rights Act by discriminating against Jacqueline Cote, a Walmart employee, based on her sex.

Walmart extended benefits to married gay couples in January 2014, just months after the Supreme Court struck down a key provision of the Defense of Marriage Act (DOMA), which defined marriage as a heterosexual union.

Cote, who works in Walmart's Swansea, Massachusetts store, was denied spousal health insurance for her wife Diana “Dee” Smithson, who was diagnosed with ovarian cancer in 2012.

The women, who have been together for nearly 23 years, married in May 2004 as soon as it was legally possible in Massachusetts, the first state to legalize such unions.

For four years starting in 2008, Cote attempted to add Smithson to her health insurance during Walmart's open enrollment periods but was denied.

By the time Walmart altered its policy in 2014, the couple had racked up a minimum of $150,000 in uninsured medical expenses.

“We want to send a message to companies big and small, that it is illegal to deny benefits to the same-sex spouses of their employees, if they provide the same benefits to employees with opposite-sex spouses,” GLAD spokeswoman Carisa Cunningham told Bloomberg.

Thomas Wassel, a corporate lawyer with Cullen and Dykman LLP who is not involved in the case, said that the case is on solid ground.

“The plaintiffs have a strong argument,” said Wassel. “A corporation does have a right to extend benefits as it sees fit, but can't do so in violation of the law.”

Brian Nick, a spokesman for Walmart, said in an email: “Our benefits coverage previous to the 2014 update was consistent with the law.”