A federal court has rejected a bid by the city electricians union's powerful political wing to keep secret details of how it spent $2.5 million last year.

The decision handed a victory to the city Ethics Board, which is investigating whether the Local 98 IBEW Committee on Political Education was behind an anonymous 2007 mayoral primary campaign flyer that portrayed Michael Nutter as a supporter of racial profiling.

The political action committee, which is known as COPE and is one of the state's richest, went to court after the ethics panel moved in November to obtain vouchers for all of its political expenditures above $25, as permitted under state law.

COPE had argued that the state campaign-spending disclosure laws violated free-speech rights, but U.S. District Judge Harvey Bartle 3d ruled otherwise Wednesday and dismissed the committee's motion seeking relief.

"We're looking at our appeal options," said George Bochetto, the attorney representing COPE.

J. Shane Creamer Jr., the Ethics Board's executive director, said the panel was pleased with the decision, which he called "clear, concise and well reasoned."

Why the board wanted to see the expense vouchers has not been made public, but in papers filed in state court in April, the panel said it was investigating COPE's possible involvement in the anonymous mayoral primary flyers.

Under state law, it is illegal to distribute campaign literature without identifying the source of the funding.

The investigation and the federal court battle became two of several subplots to emerge during electricians union leader John J. Dougherty's unsuccessful campaign for the Democratic nomination to succeed State Sen. Vincent Fumo.

Dougherty's campaign had suggested that the ethics panel's efforts were directed at getting him defeated, an idea board officials rejected.

The flyers, created by a political consultant linked to COPE, depicted a famous 1970s photograph of six men suspected of being Black Panthers being strip-searched by police. The text beneath it read, "A vote for Nutter is a vote for racial profiling" - a reference to Nutter's proposal to stop and frisk people suspected of carrying illegal firearms.

About 125,000 copies were distributed in North and West Philadelphia on primary day, the board said in its court papers.

Dougherty supported Tom Knox in the Democratic mayoral primary after deciding not to run himself.