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DENVER — Nine gay couples are expected to file a lawsuit in state court to challenge Amendment 43, Colorado’s voter-approved ban on same-sex marriage, although there is growing uncertainty that the suit will be filed Tuesday as initially indicated by the plaintiffs’ law firm.

On Monday afternoon, the law firm Reilly Pozner announced a press conference at its downtown offices at 10 a.m. Tuesday but declined to say what the suit was about, only that “nine Colorado couples, four of whom are legally married, will explain recent events that on Tuesday morning led them to file a precedent-setting civil rights lawsuit against the State of Colorado.”

FOX31 Denver confirmed through multiple sources that the plaintiffs, which include five lesbian couples and four gay couples, will be challenging the state’s gay marriage ban.

But two hours after the initial press advisory about the press conference, a second advisory followed stating that the press conference had been cancelled.

It’s increasingly unclear whether the lawsuit will be filed, or when.

Amendment 43, approved by 56 percent of Colorado voters in 2006, defines marriage in the state as a union between a man and a woman.

Attorney John McHugh is the lead attorney filing the lawsuit, along with attorneys from two other firms, in Denver district court.

“That’s so the suit can actually proceed,” a person close to the legal team explained.

Currently, there are other challenges to statewide gay marriage bans in Utah and Oklahoma in the federal pipeline, so it would be unlikely for a new suit from Colorado to move forward if it were to be filed in the federal courts.

The legal argument driving the new Colorado challenge is reportedly the same as that behind those other lawsuits: that gay marriage bans are a violation of the 14th Amendment’s Equal Protection Clause.

“Essentially this is tearing down the remaining roadblocks to gay marriage,” another source explained. “Opponents of gay marriage have lost the overall debate, and this is kind of like finishing it off.”

While the lawsuit has been put together without many of the same politicians and groups who led the fight to pass civil unions legislation last year, McHugh did call Jack Finlaw, general counsel to Gov. John Hickenlooper, to inform him of the suit last week, another source confirms.