Colorado’s constitution requires voters to approve all tax hikes or issued debt because of the Taxpayer's Bill of Rights (TABOR), an amendment passed in 1992. But some experts say Democratic lawmakers will use other avenues – such as "fees," which courts have said are exempt from TABOR – to raise revenue, a practice legislators have already taken advantage of.

Linda Gorman, an economist for the Independence Institute, told Watchdog.org that taxpayers should look out for "an explosion of ‘fees’ and off-budget government ‘enterprises’ able to issue debt along with a lot more untraditional debt that nonetheless leaves taxpayers on the hook for funding."

"In the last election, Colorado taxpayers voted down virtually all proposed tax increases. Most of the programs that the progressives they elected support cost a lot of money," she said.

In November, Colorado voters rejected Amendment 73, the Establish Income Tax Brackets and Raise Taxes for Education Initiative, which would have amended the state constitution to include a progressive income tax and exempt education spending from TABOR’s limits. Voters also rejected the "Let's Go Colorado" Transportation Bond and Sales Tax Increase, which would have raised the state sales tax for transportation funding.

Gorman added that while TABOR requires taxpayer approval to hike taxes, the state constitution "is silent on fees and government ‘business enterprises.’ To date, the Colorado courts have ruled that anything various governments call a ‘fee’ is a fee even if it walks like a tax, looks like a tax, and acts like a tax."

In May 2018, the Colorado Supreme Court ruled that the city of Aspen’s 20-cent bag charge was a fee and not a tax, which meant the fee was exempt from TABOR, a decision that some argue has undermined the purpose of the amendment.

Colorado has the nation’s 11th highest percentage of "service charges" that contribute to the state’s general revenue, according to a Pew Charitable Trust study.

"I would also expect the quality of traditional government services to fall as their budgets are raided for the new programs," Gorman said.

Jesse Mallory, state director of Americans for Prosperity – Colorado, said he expects to "see more attempts to change TABOR’s formula" in addition to attempts at increasing the state revenue cap.

"There are those who want to add more fees to capture additional revenue as well," Mallory told Watchdog.org. "I think first they’ll go after the revenue cap and the TABOR formula, and then work their way toward more direct approaches like fee increases and then maybe tax increases."

TABOR could also be debated in the courts again in the new year.

Last month, the Colorado Supreme Court rejected outgoing Gov. John Hickenlooper’s request to review the compatibility of the Gallagher Amendment and TABOR, but the court declined. Watchdog reported that Hickenlooper hoped to collect more tax revenue for the state’s struggling fire departments and to fund other public services.