Colorado's taxpayer's bill of rights was directly challenged Wednesday in federal court as state lawyers argued that a judge can't touch the amendment that voters approved in 1992. A group of state lawmakers wants the court to throw out the amendment, saying the measure strips legislative bodies of the power to tax and spend, as well as the U.S. Constitution, which designated certain powers to the branches of government. "This case is about keeping a republic," said David Skaggs, a former Democratic congressman who argued for the lawmakers. "Sadly, that form of government here in Colorado has suffered great injury." The amendment forbids state lawmakers and local elected bodies from raising taxes without a vote by the people. It also puts severe restrictions on spending, limiting officials' ability to respond in an economic downturn. A state lawyer argued that the challenge could endanger all citizen initiatives. Megan Paris Rundlet, assistant state attorney general, said lawmakers could simply ask a court to intervene if they don't like a vote of the people. "It invited this court to look at other initiatives, and other states to look at voter initiatives," Rundlet said. U.S. District Court Judge William Martinez did not immediately rule on whether to dismiss the lawsuit. Martinez posed tough questions to Rundlet. Martinez interrupted the state's lawyer often, and dismissed the state's reliance on a 1912 Oregon case upholding citizen initiatives. Martinez said the lawmakers were attacking the measure exclusively. "They're not challenging the citizens' initiative in Colorado. They're not," Martinez said. The judge also repeated a core argument of the lawmakers as he challenged the state's attorney. "Once you have a legislature that can do anything it wishes except legislate taxes, you no longer have a republican form of government," Martinez said. Skaggs argued that the taxpayer's bill of rights went too far in stripping legislative power, saying that it "didn't just dilute or impede the revenue-raising ability of the Legislature. It eliminated it." Ironically, the challenge made its first court appearance two days after the bill's architect was sentenced to jail and probation for tax evasion. Douglas Bruce, a former Republican lawmaker who has pushed other citizen initiatives, was convicted of felony tax evasion and filing false returns between 2005 and 2010. Bruce has vowed to appeal. He is to begin serving his 90-day sentence on Friday.Bruce's criminal case is unrelated to the federal lawsuit challenging the measure.