A political action committee with no formal ties to any mayoral candidate on Wednesday ran the first television commercial for the May 19 Democratic primary.

Building a Better Pennsylvania, which in the past has been funded by labor unions active in the construction industry, unveiled a 30-second ad on PHL17 that supports former City Councilman James F. Kenney's bid for mayor.

It is the first of what is expected to be a flood of campaign advertisements from independent third-party interest groups, not restricted by local campaign finance limits.

Its airing coincided with a call by Democratic mayoral candidate Lynne M. Abraham for all candidates in the race to reject such support. She asked each candidate to pledge to make a donation to the Philadelphia School District equal to any money spent on his or her behalf by a third-party interest group.

The request was immediately rejected by the five other candidates - Kenney, State Sen. Anthony Hardy Williams, Nelson A. Diaz, Doug Oliver, and T. Milton Street Sr.

The ad placed by Building a Better Pennsylvania calls Kenney "one of Philadelphia's most progressive choices," touching on his Council record on civil rights, property taxes, job creation, and accountable government. It calls Kenney "the right direction for Philadelphia."

Records on file with the Federal Communications Commission show that Building a Better Pennsylvania paid $4,750 to air the ad five times between Wednesday and next Tuesday.

Building a Better Pennsylvania spent $354,032 in the final two weeks of the 2014 Democratic primary election to support then-State Rep. Brendan Boyle's successful bid for the U.S. House.

The PAC reported after that election that 13 unions had contributed to the cause. Two-thirds of that money came from Local 98 of the International Brotherhood of Electrical Workers.

Local 98 leader John "Johnny Doc" Dougherty predicted in January that organized labor might run independent expenditure ads to support Kenney.

Chris Rupe, Local 98's director of legislative affairs, is listed as the treasurer for Building a Better Pennsylvania.

Rupe provided a statement from Wayne Miller, the PAC's chairman and the president of the Sprinklers Fitters Local 692.

"We are motivated by a strong desire to grow our region's economy and promote policies that improve the lives of our fellow citizens," Miller's statement said. "We believe Jim Kenney has the experience, vision and proven track record of progressive leadership to move Philadelphia in the right direction as its next mayor."

Building a Better Pennsylvania likely won't be alone in making independent expenditures to influence the mayor's race.

A PAC known as American Cities is expected to support Williams.

The three founders of Susquehanna International Group, a Main Line trading firm, gave $250,000 last year to launch American Cities.

Those founders - Joel Greenberg, Jeff Yass, and Arthur Dantchik - gave Williams $5 million in 2010 to run for governor because he shares many of their views on school choice.

Greenberg said in a recent interview that he and his partners had "no set dollar amount" for how much they will spend to support American Cities.

"I know they're trying to raise money from others," Greenberg said of the political action committee. "I think they've been successful as well."

The American Federation of Teachers, the national union, which represents educators in the Philadelphia School District, has said it was considering making independent expenditures in the mayor's race.

An independent expenditure group may raise and spend unlimited amounts of money - outside the city's campaign finance limits - as long as it does not coordinate efforts with a candidate or campaign.

The Building a Better Pennsylvania ad includes a disclaimer that it was "not authorized by any candidate or party committee."

Abraham anticipated there would be such support for some of her opponents when she made her call Wednesday that all candidates pledge to reject third- party involvement in the race.

Her position was resolutely rebuffed by the rest of the field.

"If we sign this, we're forfeiting the message entirely to super PACs, because making that donation would significantly deplete our campaign budget," Kenney's spokeswoman, Lauren Hitt, wrote in an e-mail. "That only heightens the influence of independent expenditures in this race."

Said Barry Caro, spokesman for Diaz: "If Jim Kenney is going to actively embrace dark money, he's gone ahead and killed the pledge."

Williams sent out a statement by e-mail.

"The pledge game is one I don't play," he said. "I think former D.A. Abraham would be better served simply telling voters where she stands rather than spending time on political PR stunts."

Angela Griffin, Street's campaign manager, said simply, "He's not going to sign that."

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