PHOENIX — Opponents of a threatened new constitutional ban on gay marriage are arguing that the real losers might not just be gays, but unmarried straight couples who could be harmed.

Sound familiar? The argument is the same one that worked to beat back a broader ban rejected by voters in 2006. But this time, the claim is dividing even those against the effort to define marriage.

Meanwhile, the group pushing the amendment says bringing straight couples into the argument is nothing but an attempt to confuse voters, since polls indicate solid public support for a straight-forward ban on gay marriage.

Still, some gay-rights advocates say the language of the new proposal is broad enough that it could put domestic-partnership and civil-union benefits offered by Arizona municipalities in jeopardy.

A possible ballot measure, which has yet to gain legislative approval, would ask voters to define marriage as between one man and one woman in the state constitution.

The 2006 ballot measure went farther, prohibiting domestic-partner benefits and civil unions, a point used effectively by opponents to defeat it.

State statute already bans same-sex marriage.

But Equality Arizona, an organization that lobbies for gay and lesbian rights, is arguing that the amendment — sponsored by state Sen. Tim Bee, R-Tucson — might go even farther than current law.

Since the proposal states, "Only a union of one man and one woman shall be valid or recognized as a marriage in this state," the groups will argue "union" could be applied to more than just marriage.

"Essentially, this amendment could take away rights from unmarried couples, gay or straight," said Sam Holdren, public-affairs director for Equality Arizona.

"We don't know how a court in Arizona will ultimately decide."

Others — including those on both sides of the argument — say Equality Arizona's argument is unsound.

Among them is state Rep. Kyrsten Sinema, an openly bisexual Phoenix Democrat who led the 2006 campaign against Proposition 107.

"As an attorney myself, I can tell you that their statement and their argument is inaccurate," said Sinema.

The successful effort Sinema led in 2006 almost totally ignored the effect that measure would have on gay couples, instead focusing on straight couples.

Peter Gentala, general council for the Center for Arizona Policy, which is pushing the measure, said proponents have no plans to target domestic partnerships with this new effort.

"Whether it's from Equality Arizona, or whatever the eventual opposition to the new marriage amendment will be, there's definitely going to be attempts to confuse the issues," Gentala said.

"Opponents of this really don't want the voters to consider the definition of marriage in a straight up or down situation — they prefer to drag in other issues," he said.

Gentala points to California, where a definition similar to the one proposed here was found to not apply to domestic-partnership benefits.

But opponents are using the same example.

Lambda Legal, a civil-rights legal organization, wrote Arizona lawmakers last month and warned them the amendment could result in years of litigation if it is passed, just as the California measure did.

"It wouldn't change the law, but it would be an incentive for folks to file lawsuits challenging domestic-partnership benefits and putting those benefits into limbo," said Brian Chase, senior staff attorney for Lambda.

And Chase said even though proponents might say the effort is only about marriage, they may change their argument after it passes.

"The proponents of the statute in California, when it was being passed, said it was all about marriage and not about domestic-partnership benefits, and then after it passed they turned around and filed suit," Chase said.

The Center for Arizona Policy did use the the language of Arizona's current same-sex-marriage ban to argue against the Arizona Department of Administration expanding benefits to domestic partners.

But Gentala said that was because the state was seeking to change policy without going through the legislative process.

State Sen. Paula Aboud, an openly gay Tucson Democrat, said the effort to defeat the ban should be focused on two issues: "We don't need any ballot initiatives, and we already have this in law," she said.

"I think we can beat it," Aboud said. "People don't want to be voting on these kinds of issues."

The issue has been delayed at the Capitol since Sinema sidetracked the effort last month.

Although Sinema and Aboud say they believe the measure doesn't have enough votes in the Legislature to make it to the ballot, Gentala of the Center for Arizona Policy says it has the support it needs.

"It's just a matter of the votes being there and having them all there in the same room healthy and ready to do," he said.

● Contact reporter Daniel Scarpinato at 307-4339 or