SACRAMENTO, Calif. (AP) – A California law that gives same-sex couples who register as domestic partners nearly the same responsibilities and benefits as married spouses should be overturned because lawmakers undermined the will of voters, lawyers for two groups argued March 25.

The law, which went into effect Jan. 1, grants registered couples virtually every spousal right available under state law except the ability to file joint income taxes. That includes access to divorce courts, automatic parental status and responsibility for each other’s debts.

The law represents the nation’s most sweeping recognition of domestic partner rights after Vermont’s recognition of civil unions for same-sex couples. New Jersey and Maine also have domestic partner registries.

Opponents of the law told a three-judge appeals court panel the law violates a California ballot initiative that defined marriage as between a man and a woman. Supporters said the law was unrelated to the ballot measure. Proposition 22 passed five years ago with 61 percent support.

“What it does is it undermines Proposition 22,” said Robert Tyler, attorney for the Proposition 22 Legal Defense and Education Fund.

Tyler and an attorney for the Campaign for California Families argued that Proposition 22’s victory in 2000 not only defined marriage, but implicitly barred lawmakers from granting marriage-style benefits to domestic partners.

The 3rd District Court of Appeal did not indicate when it would rule. The court previously rejected requests to prevent the law from taking effect during the appeal.

“The voters of the state are entitled to get what they voted on. No more and no less,” said Deputy Attorney General Kathleen Lynch in defense of the domestic partners law. “How would a voter know they were going to vote on more?”

The three justices repeatedly noted the simplicity of the 14-word ballot measure, saying it said nothing about rights of domestic partners nor the Legislature’s ability to grant them.

Presiding Justice Arthur Scotland said the appeals court typically interprets laws based on plain meaning. “If it’s plain meaning, we use the plain meaning and stop there,” he said.

The case comes in the wake of a San Francisco County Superior Court judge ruling that struck down Proposition 22 and California’s ban on same-sex marriage, saying both laws violated the civil rights of gays and lesbians to marry whom they chose.

Meanwhile, a less sweeping measure – one that would create a registry giving unmarried couples the right to make medical decision for each other – won Maryland Senate approval March 25. The bill next goes to the House of Delegates, which passed similar legislation last year.

While the bill was promoted by gay rights groups, it would apply to any unmarried couples who want to register with the state health department. Registration would guarantee partners the right to make medical decisions for each other, visit their partners’ hospital rooms, share rooms in nursing homes, share ambulance rides and make decisions about whether to bury or cremate after death.