The probe is focused on whether the timing of accepting the campaign checks created an unacceptable appearance of a conflict, according to sources familiar with the investigation and letters sent by the OCE to lobbyists requesting information. The OCE's spokesman declined to comment for this article, citing the ongoing nature of the investigation.

The office is scrutinizing five Republicans and three Democrats, a diverse group that includes a conservative, Rep. Jeb Hensarling (R-Tex.), and a liberal member of the Congressional Black Caucus, Rep. Melvin Watt (D-N.C.).

Seven of the eight members held fundraisers for their reelection campaigns on Dec. 9 or Dec. 10 -- just before the House voted Dec. 11 in favor of a bill to make broad changes in how Wall Street and financial firms are regulated, according to a Washington Post analysis. Rep. Tom Price (R-Ga.) held a "Finance Services luncheon" at the Capitol Hill Club on Dec. 10. On the same day, a lobby firm with financial clients, Davis & Harman, hosted a fundraising breakfast for Rep. Earl Pomeroy (D-N.D.) at its Pennsylvania Avenue offices.

Watt held a Dec. 9 fundraiser and soon after withdrew a proposal he had introduced to subject auto dealers to tougher regulations, according to congressional records. The fundraiser generated checks largely from finance groups, including Goldman Sachs and the Investment Company Institute. In an interview, Watt said he will answer the OCE's questions and declined to comment on the investigation.

The House ethics manual instructs members to steer away from accepting campaign donations if the timing creates an unacceptable appearance of a conflict of interest.

The other members under review are Republicans John Campbell of California, Frank D. Lucas of Oklahoma and Christopher Lee of New York and Democrat Joseph Crowley of New York.

Jamey Delaplane, partner at Davis & Harman and a former Pomeroy staff member, said his event for Pomeroy was planned seven weeks prior, when the timing of the House vote was not known. "Clearly, we had no sense this would coordinate in any way with the House financial services vote," he said.

Hensarling, a member of the House Financial Services Committee, did not have a formal fundraiser. But, according to letters, OCE investigators are asking about the 10-day period before the vote, when he raised at least $30,000 in cash from financial firms and their advocates for his leadership political action committee and campaign. "Congressman Hensarling categorically denies any implication of influence and looks forward to clearing up this false charge," spokesman George Rasley said.

Lucas and Price could not be reached for comment. Spokesmen for Campbell, Crowley and Pomeroy said the lawmakers complied with ethics rules and looked forward to a resolution of the OCE review. Lee's office declined to comment. The financial reform legislation is being worked out this week in a House-Senate conference.

Staff writer Paul Kane and research editor Alice Crites contributed to this report.