WASHINGTON -- At a hearing in late March, the nation's credit card companies faced the threat of expensive new rules from an unlikely regulator: the House Committee on Homeland Security, chaired by Rep. Bennie Thompson.

The committee had never before dealt with credit card issues, but Mr. Thompson, D-Miss., warned Visa, MasterCard and others that Congress might need to impose tighter security standards -- costing millions of dollars -- to protect customers from identity theft.

Behind the scenes, some of Mr. Thompson's staffers sensed a different motive -- an attempt to pressure the companies into making political donations to the chairman, according to several former committee staffers.

Now, the House ethics committee is investigating the propriety of the committee's operations, and whether its members' interactions with companies compromised its work. Within a few weeks of the hearing, Mr. Thompson collected $15,000 in donations from the credit card industry and its Washington-based lobbyists, a Washington Post analysis shows. No legislation on card security has been introduced.

Several former committee staffers, speaking on condition of anonymity, have told The Post that the credit card hearing was one of several committee actions that caused staff concerns because of their consideration of potential donors and contractors friendly to Mr. Thompson. The current ethics inquiry was prompted this summer, according to an ethics document obtained by The Post, when a former committee aide alleged that she was fired after complaining to her bosses that a lobbyist made improper requests of staff members.

Mr. Thompson -- who made headlines separately this week by calling a committee hearing to investigate Tareq and Michaele Salahi's ability to get past Secret Service and into a White House state dinner without invitation -- said he did not arrange a hearing to generate campaign donations. "That's incorrect," he said of the suspicion. "We do hearings all the time -- sometimes we are able to generate legislation earlier, and sometimes we have to make [build] a public record."

He added that he has never been told of staff complaints about his hearings, and was unaware that a committee staffer said she was fired for raising objections about inappropriate lobbyist requests. "I would assume, if discomfort was there with the staff, they would have shared it, " he said. "I have not heard this."

Committee staff director Lanier Avant, who also serves as the congressman's chief of staff, said the credit card hearing was prompted by a data breach at a payment company, Heartland Payment Systems, that compromised the credit information of millions of customers.

Several congressional ethics experts said it could be an ethics violation if a lawmaker or senior staff member arranged a hearing for the express purpose of collecting campaign contributions. Proving such a case would be difficult, they said.

Numerous credit card lobbyists, asked about their donations, would not comment for the record. Officials at Visa and the industry-sponsored Payment Card Industry Council, who were asked to testify at the hearing, said they were unaware of the staffer's allegation and did not have concerns about the hearing.

In April and May, donations of $250 to $1,500 came in from lobbyists registered to represent Visa, American Express, MasterCard, Heartland and the National Installment Lenders, among others, as well as from the American Bankers Association political action committee.

Washington correspondent Daniel Malloy writes the "Pittsburgh On The Potomac" blog exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.