HELENA (AP) — A Montana university system policy denying health insurance coverage to employees’ same-sex partners is an attack on gays and lesbians that should be outlawed as unconstitutional discrimination, the American Civil Liberties Union told the Montana Supreme Court.

In written arguments filed with the high court, the organization said the policy is based solely on a person’s sexual orientation and cannot be justified by the government.

“It is hard to imagine how denying equal benefits to gay employees and their life partners promotes any state interest at all, much less a legitimate one,” wrote ACLU attorney Holly Franz of Helena.

The legal arguments are the latest development in a court case that began more than a year ago when a lawsuit was filed by Carol Snetsinger and her partner Nancy Siegel, and Carla Grayson and her partner Adrienne Neff.

Grayson’s and Neff’s Missoula house was destroyed by an arson fire shortly after the lawsuit was filed. No arrests have been made.

Snetsinger and Grayson, who work at the University of Montana, charged the university system unfairly denied their domestic partners health insurance offered through UM.

UM offers health insurance only to employees, their spouses and children. Heterosexual couples who are not married, but file an affidavit of common law marriage, can also qualify for coverage.

But same-sex couples are barred by law from marrying so they cannot obtain health insurance for partners through the university system.

Last November, District Judge Thomas Honzel of Helena ruled in favor of the system, agreeing with its arguments that the health insurance policy is based on the marital status of employees, not on their sexual orientation. He said that is a “reasonable and objective standard” for determining who qualifies for employment benefits.

The state will file its response in the appeal later.

In her written arguments, Franz contended that the policy is really about gays and lesbians because they are the only ones unable to get coverage from the university system.

She said defendants “offer unmarried different-sex couples a choice: Tell us you are committed to one another or forego dependent benefits. Defendants offer same-sex couples no such choice.”

“No gay couple can obtain dependent benefits while all heterosexual couples have the opportunity to obtain benefits,” Franz said. “No matter how they slice it, defendants’ policy makes eligibility for benefits depend on sexual orientation.”

Such a practice denies gay and lesbian employees equal protection of the laws and subjects them to sex discrimination for which the state has no compelling interest in practicing, Franz said.

She suggested the policy is meant to put gay and lesbian couples at a disadvantage and to morally condemn same-sex relationships. That, she said, is a violation of the fundamental constitutional rights of human dignity, privacy and the pursuit of life’s basic necessities.