A radio ad from a super PAC backing Acting Mayor Kim Janey is drawing criticism from its target, District 4 Councillor Andrea Campbell, and causing a firefight between the two mayoral campaigns.

Linked to the hotel workers union UNITE HERE Local 26, which endorsed Janey in the five-way race, the super PAC has spent $34,200 on a 30-second radio ad attacking Campbell and a pro-Campbell super PAC, known as “Better Boston.”

Each of the mayoral candidates has at least one super PAC, which is an outside group that can raise and spend unlimited amounts of money but it is prohibited from coordinating with the campaigns. Overall super PAC spending has soared past $2.1 million for the 2021 Boston mayoral race.

“Money talks, Andrea Campbell listens. Andrea Campbell’s campaign for mayor is supported by special interests that want to take money from our schools and give it to other schools that discriminate against kids with special needs,” the male narrator said in the hotel workers super PAC’s ad. “Special interests versus kids with special needs. Andrea Campbell is on the wrong side.”

At a press conference in Grove Hall, Campbell called on Janey to “disavow” the union’s super PAC, which she said is spreading “lies and misinformation” through the negative ad.

“The acting mayor's super PAC is actually putting out attack ads right now, specifically naming only me and perpetuating lies about my record of accomplishment, about my candidacy and my stance on education and so many other issues,” she said. “And I tell folks, don't be distracted by the noise. Don't be distracted by the lies or the fear-mongering.”

Campbell added: “I’m the only candidate that actually has represented students with special needs in education cases, sometimes against Boston Public Schools, to ensure they got the rights they were entitled to.”

Asked by reporters about some of the “Better Boston” donors supporting charter schools, Campbell said the super PAC has other donors, including Nonnie Burnes, a state judge who recently passed away. Burnes, who worked as Gov. Deval Patrick’s insurance commissioner, was a “fierce” advocate for reproductive rights, Campbell said.

Campbell said she supports Boston Public Schools and wants to improve the system so her children don’t have to go to another system or charter schools.

Janey, who denounced super PACs early in the race but throttled back the criticism when she got her own outside group, lashed back at Campbell through her campaign manager.

“Andrea Campbell’s entire campaign is based on negative political attacks on Mayor Janey, so it’s the height of hypocrisy for her to complain about an outside group providing voters with information about her,” Kirby Chandler, Janey’s campaign manager, said in an emailed statement. “Instead of attacking hotel workers for expressing their political views, Campbell should condemn the dark-money, right-wing millionaires who want to privatize our public schools and have poured millions of dollars into TV ads supporting Campbell’s campaign.”

The hotel workers super PAC put out its own statement taking aim at Campbell before the councillor’s Tuesday morning press conference got underway.

“Andrea Campbell worked for notorious anti-union ‘lockout lawyer’ law firm Proskauer Rose,” the hotel workers super PAC said in its statement. “Her campaign is supported by a Super PAC dripping in donations from those who want to take money out of BPS schools. Compare that to Kim Janey’s campaign that is supported by hotel workers, janitors, and Stop & Shop workers. That is the issue here.”

The hotel workers super PAC is also paying to air a positive radio ad about Janey, referring to her comments invoking birtherism and slavery when asked about vaccine passports.

“Leadership isn’t easy. Mayor Kim Janey’s focus on equal access to vaccines caused her to say things she regrets,” a female narrator said in the ad. “But Mayor Janey is getting our community vaccinated and wants us to wear a mask to protect one another. Kim will do whatever it takes to protect us. Stay safe. We are strong.”