Three Philadelphia labor unions - the Philadelphia Federation of Teachers, the Ironworkers and the Sprinkler Fitters - have kicked in $64,500 to run independent television ads against mayoral candidate Tom Knox.

But the group to which they sent their contributions - the Economic Justice Coalition for Truth - is still looking for a television station willing to run the ads.

Under pressure from the Knox campaign, which has showered millions of dollars on the local television stations over the past six months, channels 3, 6 and 10 all have refused to run a 30-second spot criticizing Knox's past business dealings.

The spot was produced by political consultant Ken Smukler, who was working for the campaign of mayoral rival Bob Brady until last week.

WPVI (Channel 6) spokeswoman Caroline Welch said the station wanted more documentation of the group's charges against Knox.

Eva Blackwell, a spokeswoman for NBC 10, said the station's lawyers had decided the spots were not "appropriate." She said she had no further information.

The 30-second spot is based on stories in the Daily News and Inquirer describing three events in Knox's business career: a $70,000 fine by the Maryland insurance department for violation of state insurance regulations, one of which involved advising policyholders to consult their primary physician before seeking treatment in an emergency room; a $28,000 fee taken as a broker on insurance policies for the Pennsylvania Convention Center; and the charging of consumers as much as 400 percent annualized interest on short-term "predatory" loans.

Attorney Alex Talmadge Jr., treasurer of the anti-Knox group, said the Coalition for Truth would pursue a three-pronged legal strategy - asking the Philadelphia TV stations to stop running a Knox ad that refers to the anti-Knox group as "illegal"; preparing a defamation suit against Knox, his campaign and his attorney; and filing a complaint with the Federal Communications Commission against the local TV stations.

"There is nothing illegal about our ad," Talmadge said. "It is all substantiated."

The three contributors to the fund were identified yesterday for the first time, in a campaign-finance disclosure required by state law.

The teachers' union provided the bulk of the money, a $50,000 donation. Ironworkers Local 401 contributed another $7,500 and the Sprinkler Fitters Local 629 added $7,000.

The report covered from April 4, when the group was created, through April 30. Under state law, any additional contributors need not be identified until 30 days after the May 15 primary. *