PORTLAND, Maine (AP) A U.S. military veteran and his daughter filed a lawsuit on Monday challenging a federal rule they said prevents the daughter from accessing medical coverage because she is transgender.

The veteran and daughter filed their lawsuit against the government anonymously via GLBTQ Legal Advocates & Defenders, a Boston-based advocacy group. The group’s court filing said the daughter has been denied treatments recommended by doctors due to a federal statute that dates to 1976 that mandates exclusion of surgical treatments for gender transition in the military’s medical coverage for dependent of service members.

The statute is an antiquated rule based on outdated views of transgender people, and striking it from the books would be significant for many people seeking to access care, said Ben Klein, an attorney with GLAD.

“We can safely say this is the first time the statute has been challenged. It would affect a huge number of people,” Klein said. “A victory in this case would ensure that all dependents of military personnel who are transgender would have access to the critical medical care they need, free of discrimination of exclusion.”

The defendants in the lawsuit include the U.S. Department of Defense and Defense Secretary Lloyd Austin. The plaintiffs, who live in Maine, filed their lawsuit in U.S. District Court for the District of Maine in Portland. The lawsuit calls for the exclusion rule to be declared unconstitutional and also states that the plaintiffs want damages.

Representatives for the U.S. Department of Defense declined to comment on the lawsuit and deferred to the U.S. Department of Justice, which would represent the agency in the case. Justice Department representatives did not immediately respond to a request for comment from The Associated Press.

The lawsuit states that the veteran served for 23 years in the Marine Corps and Air Force. His daughter is a 21-year-old transgender woman who has been diagnosed with gender dysphoria and sought gender transition surgery to address the condition, the lawsuit states.

The suit states that the daughter, who is only referred to as Jane Doe, is entitled to receive health care benefits through the military’s TRICARE health plan, which is a program of the Defense Department’s Military Health System. It states that she “has been and continues to be unable to obtain coverage as a TRICARE beneficiary” for gender transition surgery because of the 1976 rule.

The lawsuit states that the daughter has also incurred costs and sought alternative health insurance because of previous improper denials of coverage by the defendants. Her request for coverage of treatments including laser hair removal and electrolysis were previously denied, the lawsuit states.