Udall made his position known Tuesday night in The Denver Post Senate debate where he and Republican Congressman Cory Gardner squared off.

One of the yes/no questions the pair was asked was about the 1992 voter-approved ballot measure that controls taxation and spending in Colorado. Should it be changed or altered?

Gardner said “no,” a stance adopted by many conservative Republicans over the years. Udall also said “no.”

“You’re kidding,” said former lawmaker Norma Anderson, a Lakewood Republican who is part of a bipartisan group of current and former state legislators and local officials challenging the constitutionality of TABOR in federal court.

“I’ll be damned.”

The suit alleges that TABOR, which prohibits the legislature from raising taxes without a vote of the people, limits the General Assembly’s power in violation of the U.S. Constitution guarantee that states have a “republican” government, in which the authority to govern is given to elected officials. The plaintiffs argue in court filings that TABOR has caused “a slow, inexorable slide into fiscal dysfunction” in Colorado.

Gardner called out Udall on his TABOR answer.

“I find it curious that Sen. Udall supports TABOR when he actually has supported tax increase after tax increase at the state level,” he said, during the debate.