Plans for a measure that could repeal marijuana legalization in Colorado have lost momentum at the state Capitol, according to lawmakers and advocates involved in the debate.

Last week, several legislators confirmed they were working on a proposal that could overturn marijuana legalization if voters do not approve new taxes on legal pot this November. Supporters of the idea said, without the tax money, the state can’t adequately pay for enforcement of forthcoming recreational marijuana stores.

But talks on the plan have proved difficult, throwing into question whether it will even be officially introduced.

“I think people are counting their votes,” said House Speaker Mark Ferrandino, a Denver Democrat who didn’t endorse the repeal proposal but previously said he was open to the discussion. “I think there are people on both sides who have concerns about it.”

Ferrandino said proponents have now scaled back the plan. Under the latest draft proposal, commercial marijuana sales in Colorado would be put on hold until voters approve extra taxes on the sales, Ferrandino said.

Rep. Frank McNulty, a Highlands Ranch Republican who supports the repeal idea, said lawmakers may not have the time to pass the possible measure.

Opponents of the idea, he said, “could drag the (proposal) out to the point where they make it difficult to pass.”

This year’s legislative session ends next Wednesday, and any measure would have to be introduced by Monday morning to have even a glimmer of hope of passage.

In November, Colorado voters approved a constitutional measure that legalizes use and possession of up to an ounce of marijuana for people 21 and older. The measure also allows for marijuana to be sold in specially licensed stores.

At the Capitol, lawmakers have proposed a bill that places a 15 percent excise tax and an initial 10 percent extra sales tax on marijuana. The bill, House Bill 1318, is on-track for passage, but voters in November would ultimately have to OK the new taxes.

The marijuana legalization repeal — or suspension — proposal would also have to be approved by voters. But, before it could reach the ballot, it would need two-thirds support in the Capitol because it would change a provision of Colorado’s constitution.

Rep. Dan Pabon, a Denver Democrat opposed to the plan, said many lawmakers have lost interest in the repeal idea.

“There was a pretty strong grassroots response that I think every member received that said, ‘Don’t threaten us,'” Pabon said.

A legal analysis released this week by proponents of marijuana legalization also raises more possible problems for the repeal plan. The analysis, by attorney Edward Ramey, says the Colorado constitution allows only fiscal measures to go before voters statewide in odd-year elections.

Ferrandino, though, said the legislature’s attorneys concluded it would be constitutional to put the idea before voters this year.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/john_ingold