Roughly 200 people filled the old Supreme Court chambers to hear debate.
Democrats passed the law last year after mass shootings in Aurora and Newtown, Connecticut, but faced a conservative backlash that fueled the recall of a pair of Democrat lawmakers.
Backers of the repeal say the checks are onerous and infringe on 2nd Amendment rights.
Karina Vargas, a gang-shooting survivor, came to the hearing in a wheel chair.
Vargas says she believes expansion of background checks helps stop more violence.
“There’s many other situations that have happened that they’ve gotten guns without a background check," Vargas said. "And it probably would have prevented a lot of other tragedies.”
But backers of the repeal like the bill's sponsor Pueblo Republican Senator George Rivera say the checks are "burdensome."
“They’re being made to inconvenience themselves, pay a fee in order to purchase a handgun and like I say again, or a weapon, and that’s a right that’s guaranteed by the Constitution," Rivera said. "So, it’s an infringement, that’s the bottom line to it.”
The hearing lasted several hours with roughly equal numbers of supporters and opponents of the bill testifying.
Democrats argue state statistics show the new law has prevented more than 100 criminal offenders from obtaining firearms since July.