As a stealth group prepared to launch TV ads attacking Philadelphia mayoral candidate Tom Knox, a civic watchdog organization yesterday labeled this effort a "brazen attempt to avoid the city's campaign-finance law."

The nonpartisan Committee of Seventy called on the city Board of Ethics to investigate the group's assertions that it is not connected to any of Knox's four rivals in the May 15 Democratic primary, or to the city's Democratic Party.

"When the purported mission of a committee is simply to attack a candidate, you have to ask whether that committee is crossing the line," said Seventy's president, Zack Stalberg.

Shane Creamer, interim chief of the ethics board, said last night: "The board is aware of the new committee and is checking to see who is behind it."

Lawyer Abbe Fletman, speaking for the anti-Knox committee, said "everything we're doing is legal."

The Committee of Seventy's criticism came as a second former Democratic officeholder bashed Knox's business record at a City Hall event organized by the so-called 527 committee, named the Economic Justice Coalition for Truth.

Citing an Inquirer story, former City Councilman Ed Schwartz gave a PowerPoint presentation to highlight Knox's past role in a bank that made high-interest "payday" loans. Schwartz also criticized Knox for likening federal bank regulators to "Gestapo."

Schwartz said he was asked to speak by the 527 committee's lawyer and executive director, Democrat Alex Z. Talmadge Jr., a former city commissioner who ran for district attorney in 2001. The committee paid the tab - Talmadge said he did not know how much - to rent a City Hall room for yesterday's event.

Talmadge and the Rev. Robert Shine, a former head of the Black Clergy of Philadelphia and Vicinity, head the 527 committee, which is similar to one that sprang up during the 2004 presidential race. Named for a section in the federal tax code, such groups can attack or defend candidates but cannot coordinate their efforts with a candidate's campaign.

In papers filed with the IRS April 4, the group said its purpose was "exploring the issues of economic justice as they relate to the business practices" of candidate Knox.

The group does not have to disclose its donors or expenses until July 31 - well after the May 15 primary. But Talmadge said it would soon register with the state as a political committee, a move that may force it to reveal its donors sooner.

For now, Talmadge, who appeared with Schwartz yesterday, described the group's backers as "individuals who care about working-class people across Philadelphia." He said the group was "in the process of reserving TV time."

Talmadge acknowledged that he had stood in for Knox rival Bob Brady, who chairs the city's Democrats, at a campaign forum several weeks ago, but stressed the committee was acting on its own, as did Brady spokeswoman Kate Philips in a telephone interview. "It would be not only illegal but incredibly stupid to focus on some other group when you have a campaign to run," she said.

Talmadge revealed the name of another lawyer involved in the 527 committee: Fletman, who filed the group's papers with the IRS. Fletman served as a lawyer to Mayor Street's 2003 campaign, and to the campaign of Jonathan Saidel, who quit the race in January and now backs Brady.

This time around, Fletman said she was backing Democrat Chaka Fattah, but not advising him. His campaign, too, said it had no tie to Talmadge's group.

The group has surfaced at a time when Knox's rivals contend the city's strict contribution caps - $5,000 from individuals, $20,000 from political committees - bar them from matching the millions of dollars Knox is spending on his candidacy.

"I may send a check from my own personal checking account," said local NAACP leader J. Wyatt Mondesire, a supporter of one of Knox's rivals, State Rep. Dwight Evans.