A proposal that could lead to the repeal of marijuana legalization in Colorado has gained momentum at the state Capitol.

The repeal would be linked to a measure on marijuana taxes that is expected to go before voters in November, according to legislators and advocacy groups involved in the discussions. The premise is that, if voters do not approve the taxes, then Amendment 64, the initiative passed just months ago to legalize marijuana, would be repealed. It’s also possible that voters would be given a choice of repealing marijuana legalization if the taxes don’t pass.

After only a few days of behind-the-scenes talks, the proposal emerged publicly Friday. The leaders of both chambers are receptive to the plan.

House Speaker Mark Ferrandino, D-Denver, called the plan “worth the conversation.”

“I’m open to it,” he said.

Senate President John Morse, D-Colorado Springs, went even further.

“I am absolutely supportive of the idea,” he said.

The leaders’ backing is significant since the measure faces a tough road out of the legislature. Because it could repeal a constitutional amendment, the proposal needs two-thirds support to go before voters. It must also navigate through an increasingly acrimonious atmosphere at the Capitol with only 12 days left in the session.

Just about everything surrounding the measure is, for now, uncertain and disputed.

Rep. Frank McNulty, a Highlands Ranch Republican who is involved in the repeal talks, said lawmakers who support the idea haven’t agreed on final language for a repeal proposal. The plan hasn’t been officially introduced, either.

Rep. Dan Pabon, a Denver Democrat who has been involved in many of the discussions on marijuana at the Capitol this year, said the repeal idea would undermine good-faith efforts to regulate marijuana.

“I’d hate to see all the hard work we’ve done to protect public safety go to waste,” Pabon said.

Tensions over the proposal are also high between supporters of marijuana legalization and a group working to restrict pot in Colorado. Back-to-back news conferences by the groups outside the Capitol on Friday devolved into direct exchanges of heated words between advocates on both sides.

“What this comes down to is extortion,” Mason Tvert, one of Amendment 64’s authors, said during his news conference. “The proposal to repeal Amendment 64 is extortion.”

“If the taxes are passed in the fall,” said Diane Carlson, a member of the marijuana-critical group Smart Colorado, “there should be no concern about the repeal. … I don’t see why everybody is so scared about being held accountable.”

Amendment 64 legalized use and possession of up to an ounce of marijuana for people 21 and older in Colorado. It also allows marijuana to be sold in specially licensed stores, which could open at the start of 2014. Voters approved Amendment 64 in November with 55 percent support. It garnered more votes in the state than did President Barack Obama.

The amendment allows lawmakers to propose up to a 15 percent excise tax on marijuana to generate money for school construction, and lawmakers have also proposed a 15 percent special sales tax on pot to pay for regulation of marijuana stores. The tax proposals, contained in House Bill 1318, passed the House Appropriations Committee on Friday morning.

Lawmakers have publicly worried about how the tax plan, which could generate tens of millions of dollars annually, would fare with voters. If voters don’t pass the plan, the fear goes, marijuana regulations will be underfunded and ineffective.

“Without this measure, we won’t be able to implement a model that will ensure our communities can be kept safe,” Rep. Jonathan Singer, the Longmont Democrat sponsoring HB 1318, said during a committee hearing Thursday.

McNulty said attaching the taxes to a repeal provision would give marijuana advocates “skin in the game” to push for the tax measure. Carlson agreed, calling a repeal threat “the only way of ensuring there will be tax money to fund the regulatory costs.”

But representatives for Smart Colorado sent mixed signals as to whether they would urge voters to approve the taxes if they were tied to a repeal.

Tvert, meanwhile, said that if lawmakers are worried voters won’t approve 15 percent excise and sales taxes, the tax proposals should be shrunk. He suggested a 10 percent sales tax, and cited a poll Amendment 64 backers commissioned that shows 77 percent support in Colorado for that level.

Several lawmakers have also suggested the proposed tax rates be lowered.

“I don’t think the voters will accept that,” Rep. Brian DelGrosso, R-Loveland, said during Friday’s committee meeting of the 15 percent rate.

Singer, though, said — if voters approve the tax measure — lawmakers can ultimately set the rates at lower levels.

“This is our best educated guess on how to proceed,” he said.