Nearly a dozen states are hoping the U.S. Supreme Court lets Arizona deny benefits to the domestic partners of state employees. A federal court last year it was illegal to say only spouses and dependents of married state and universities were eligible. The judges said that denies equal rights to gay workers, who cannot marry in Arizona.

Indiana Solicitor General Thomas Fisher says states are entitled to promote marriage because it "channels sexual desires capable of producing children into stable unions."

But Tara Borelli, who represents gay state workers, says that has nothing to do with marriage.

"This is a narrow case. Just looks at one issue. And that is, as a basic matter of workplace service, are gay and lesbian employees entitled to the same compensation as everyone else in the form of family coverage," Borelli said.

James Campbell of the Alliance Defending Freedom notes the appellate court ruling hinged on the inability of gays to marry in the state, which he says sets a precedent.

"If it's irrational to give that benefit to only legal spouses and not to an unmarried partner or friend, then it is also irrational to also give other benefits to a legal spouse or not to an unmarried friend or partner," Campbell said.

Campbell says that could set the stage for the appellate court to say there is no rational basis for limiting marriage solely to those of the opposite sex.