Supporters of the Taxpayer’s Bill of Rights in Colorado have something new to worry about after the federal 10th Circuit Court Court of Appeals on Monday gave new life to an eight-year-old lawsuit seeking to nullify it.

The 2-1 decision reverses a ruling two years ago by the U.S. District Court in Colorado, which dismissed the case targeting TABOR.

A collection of local officials filed the suit in 2011, saying the state constitutional measure’s cap on taxing and spending violates the U.S. Constitution, which gives tax-setting power to a representative, or republican, form of government.

The merits of the argument, however, have not yet been tested.

The case has been stalled over whether local agencies such as a county commission and school districts have “standing” — meaning they suffer a direct impact — to bring the case against TABOR.

> RELATED: INSIGHTS | TABOR a target unless Supreme Court puts it out of reach

“Citing a variety of reasons, the district court declared it ‘does not believe’ that the requirement of a Constitution ‘republican in form’ stretches to the political subdivision plaintiffs,” Monday’s appeals-court ruling states. “But each proposed rationale is insufficient to extricate the standing inquiry from the case on the merits, which is not presently before us on this appeal…”

Voters put TABOR in the state constitution in 1992. It requires the government to issue rebates or future discounts to taxpayers, whenever the state collects revenue beyond TABOR’s formula. Voters have to decide on new taxes and any long-term borrowing repaid with tax dollars.

Barring more appeals, the merits of that case could soon be argued.

But by then it could be moot.

Voters this November could be asked to repeal TABOR if opponents move ahead with a proposed ballot measure that the state Supreme Court has ruled passes muster under the state constitution.

> RELATED: Colorado Supreme Court rules TABOR repeal can go forward

Separately, Democratic legislators this spring referred Proposition CC to the ballot, asking voters to decide whether to forego future refunds so that money could be used for education and transportation. The bill had just one Republican supporter, Sen. Kevin Priola of Henderson.

In yet another TABOR case, the Colorado Supreme Court heard arguments last month on whether fees should be treated like taxes under TABOR.

“We are confident that TABOR will ultimately be upheld,” the TABOR-defending conservative advocacy organization Colorado Rising Action said in a statement Monday. “People give government its authority, and Coloradans again and again choose having a say on tax increases and the size of government. Not only has this law benefited our state, but it is enormously popular.”