A Michigan appeals court ruling that bans public universities and state and local governments from providing health insurance to partners of gay employees has alarmed gay rights advocates nationwide.

They fear the decision could encourage similar rulings in 17 other states whose bans on gay marriage could be interpreted to prohibit domestic-partner benefits for same-sex couples.

Michigan last week became the first state to rule that public employers cannot offer health benefits if the benefits are based on treating same-sex relationships similar to marriage.

"It really is just a matter of time before we start seeing wholesale litigation in this area," said Carrie Evans, state legislative director for the Human Rights Campaign, a gay rights group in Washington.

In Alaska, the only other state to rule on the benefits given to same-sex partners of public employees, the courts ruled the other way, saying it was unconstitutional to deny them.

More than 20 other states have yet to decide how their gay marriage bans apply to same-sex partner benefits.

Dennis Patrick, a professor at Eastern Michigan University, worries that Michigan's ruling will strip his partner's health insurance.

The couple have adopted four children, one with a developmental disability, and Tom Patrick works part-time so he can care for them.

"If he has to go back to work full-time, that hurts our family. Or we have to pay for health benefits out of pocket, which hurts our family," Dennis Patrick said. "To me that either demonstrates a lack of understanding of how this can affect our family or other families, or it's just mean and cruel."

He is one of 21 plaintiffs who sued the state. They will appeal to the state Supreme Court.

Twenty-seven states have passed constitutional bans on gay marriage, mostly since 2004 in response to gay marriages being performed in Massachusetts. Eighteen of them, including Michigan, have broader amendments that also prohibit the recognition of civil unions or same-sex partnerships.

Still, Michigan's appeals court decision caught some by surprise.

"This is pretty unprecedented," said Jeffery Montgomery, executive director of the Triangle Foundation, a gay rights group in Michigan. "It just seems like such a needless slam on gay and lesbian families. The health and livelihood of their families is at stake in this ruling."

Conservatives, however, are lauding the decision and say the amendment's wording was clear.

"Since two-thirds of all the marriage amendments are more similar to Michigan's language, who's to say that the Michigan decision won't be the prevailing precedent in the future?" said Gary Glenn, the president of the American Family Association of Michigan who helped write that state's measure.

At least 375 university and government employees in Michigan could be affected by the ruling, according to a survey of public employers by The Associated Press. Numbers weren't available for two school districts and two community colleges.

Other states are examining the reach of their gay marriage bans.

The Ohio Supreme Court is considering whether the state's amendment prevents domestic violence charges against unmarried people. A county judge threw out an Ohio lawmaker's lawsuit challenging Miami University's same-sex partner benefits policy, saying he had no legal standing to sue. But the issue could crop up again.

Three lesbian couples this week sued to force New Mexico to provide health insurance to partners of state retirees. University of Wisconsin officials have said that state's amendment makes it unlikely the Legislature will add health insurance benefits for domestic partners.