Democrats who argued against the bill said it usurps local control and goes against the wishes of people who turn over their unwanted weapons to keep them out of the hands of children or thieves.
Buybacks are popular among some police and elected officials who either pay cash or hand out gift cards in exchange for weapons. Tucson and other Arizona communities destroyed weapons from the events, arguing that because the guns were voluntarily surrendered, the laws concerning weapons seized by authorities didn't apply.
House Bill 2455 prompted a furious debate in the state Senate, where Democrats accused Republicans of complaining about an overbearing federal government but then turning around and dictating policies to local governments.
Brewer's office did not release any signing letter accompanying the announcement of more than 30 bill she signed Monday evening, but the Republican governor is a strong gun-rights supporter and had signed the 2010 and 2012 laws.
The governor's office said it received nearly 2,000 letters, emails or phone calls about the bill, with only 25 opposed.
One of the letters in support was from the National Rifle Association, which argued that selling seized or forfeited guns "would maintain their value, and their sale to the public would help recover public funds." The NRA letter said the bill doesn't prevent a private group from holding an event and destroying the weapons.
"However, this measure would ensure that taxpayer resources are not utilized to pursue a political agenda of destroying firearms," according to the letter, sent April 22 and signed by Brent Gardner with the NRA's Institute for Legislative Action.
Maricopa County Supervisor Mary Rose Wilcox, a Democrat who champions the buyback events and survived being shot in the buttocks at the end of a 1997 Board of Supervisors meeting, sent a letter to Brewer urging a veto.
The bill "would force the resale of guns that would otherwise never have been used for violence," she wrote. "How many lives would be lost through the use of weapons our citizens hoped to be removed from the hands of criminals?"
A second bill signed by Brewer on Monday bars cities, towns and counties from collecting or maintaining any identifying information about a person who owns or sells a firearm.
Copyright 2013 The Associated Press.