(CNN) -

A Democratic Milwaukee mayor who will face an incumbent governor in Wisconsin's recall election engaged his rival in a heated debate Thursday over a campaign ad about homicide records in the city.

Mayor Tom Barrett and Gov. Scott Walker were participating in their second debate before the June 5 gubernatorial recall vote.

Barrett is facing Walker in a recall election after the latter made a controversial decision in 2011 to cut most collective bargaining rights for state employees.

A poll released Wednesday indicated the Republican governor holds a seven point advantage over his Democratic challenger.

In Thursday's debate, Barrett said Walker should be "ashamed" of an attack ad that suggests the mayor misrepresented his city's crime rate.

"It was a bureaucratic mistake and we said we'd fix that," Barrett said. "And you're running a commercial attacking my integrity, saying I had something to do with this. And you know that's false. You know that's false. And you're running that commercial."

Barrett added, "I'll tell you right now I had nothing to do with that. You should be ashamed of that commercial, Scott Walker."

Walker explained his campaign spot was meant to call into question his opponent's claims of cutting crime.

"The reason we're pointing that out is that all through the primary campaign, you told the people of this state that one of the key reasons people should vote for you is because your leadership in the city of Milwaukee brought about a drop in violent in crime. Violent crime has not gone down," Walker said.

Wisconsin's recall election came after a battle in the state over collective bargaining rights for state workers.

Walker and GOP allies in the Wisconsin state legislature voted in January 2011 to limit raises for public employees, except police and firefighters, to the rate of inflation. They also moved to bar unions from deducting dues from workers' paychecks.

That bill was signed into law in March, following protests at the Capitol.

Unions argued that collective bargaining -- a process of negotiations meant to regulate working conditions -- has served to protect their wages and health care, as well as enforce workplace safety and serve as a means to arbitrate employee grievances.

Walker, along with other supporters of the measure, asserted union contracts constrain efforts to address Wisconsin's swelling deficit.

On Thursday, Barrett characterized the reforms he made on collective bargaining rights as necessary and effective, saying the lack of discussion of the reforms in the recall election pointed to their success.

Asked what the meaning of the recall election was, Walker said he thought "it's ultimately about whether or not we want politicians to act on tough decisions."

"That's exactly what we did," Walker continued. "It's interesting that for all the talk of what the recall was initially, we don't hear a lot about that anymore. It's because our reforms are working."

Barrett disagreed, saying the cuts to bargaining rights were a measured bid to turn Wisconsin into a "right-to-work" state by putting major restrictions on labor unions.

Barrett, as he has before, classified Walker as a "rock star" for tea party interests that put his own political ambition ahead of his state's well-being.

"Scott Walker started this civil war," Barrett said. "He started this civil war, and quite honestly you know and I know that if you accepted, back in February 2011, the offer from employees to allow them to pay towards their health care and their pensions, we wouldn't be sitting here tonight."