The Federal Election Commission voted Thursday to let Rep. Peter J. Visclosky use campaign money to pay the legal bills of aides in connection with an ongoing federal investigation of the former lobbying firm, PMA Group.

But at least one commissioner raised concerns that the ruling would also cover Rich Kaelin, a former top Visclosky aide who left the Indiana Democrat six years ago to become a lobbyist for PMA.

“The chief of staff is a former employee of both of the entities under investigation — Rep. Visclosky as well as the PMA Group,” said Chairman Steven T. Walther, a Democrat. “Some of the major contributions that appear to occurred  . . .  were when he was employee of the PMA Group.”

In June, the agency cleared Visclosky to use campaign funds to for his own legal fees associated with the PMA probe and a House ethics committee inquiry in complaints that some members of Congress may have received questionable donations from PMA lobbyists and their clients. Thurday’s decision marked the first time that the FEC had allowed campaign funds to help cover the legal expenses of candidates’ current and former staff members.

Walther wanted to bard Visclosky’s campaign funds from being used to help Kaelin, who worked as a lobbyist for the PMA Group until it was disbanded earlier this year. The other five commissioners refused to go along, and voted instead to place no limitations on Visclosky.

“It is not our job to decide that sort of thing, though I agree with (Walther) in spirit,” said Republican Commissioner Donald F. McGahn II.

In addition to serving as Visclosky’s chief of staff between 2000 and 2003, Kaelin was the congressman’s main staffer on the Appropriations Committee. Later, Kaelin became one Visclosky’s largest individual campaign contributors.

Kaelin and his wife, for example, have donated $32,000 to Visclosky’s personal campaign fund and his political action committee. Calumet PAC, since 2004, according to a CQ MoneyLine analysis of FEC reports.

Lobbying disclosure records and a review of earmarks also show that Kaelin represented a dozen PMA clients that received more than $20 million in earmarks from Visclosky in the fiscal 2008 Defense appropriations bill.

Kaelin did not return phone calls seeking comment.

Visclosky campaign spokesman David St. John said the congressman “sought permission from the FEC to exercise his own discretion to use the campaign funds for the legal expenses of staff members in connection to the PMA matter.”

The FEC decision potentially could apply to dozens of former Visclosky aides who may have been subpoenaed or questioned in connection with the PMA investigation. But St. John said that the congressman’s request would not apply to aides who left the lawmaker’s employ prior to this year.

“The congressman intends for this to cover those who are on his staff and those who were on his staff earlier this year when this matter became known,” St. John said.