The Office of Congressional Ethics is investigating the chairman of the House Financial Services Committee over possible violations of insider-trading laws, according to individuals familiar with the case.

Rep. Spencer Bachus (R-Ala.), who holds one of the most influential positions in the House, has been a frequent trader on Capitol Hill, buying stock options while overseeing the nation’s banking and financial services industries.

The Office of Congressional Ethics, an independent investigative agency, opened its probe late last year after focusing on numerous suspicious trades on Bachus’s annual financial disclosure forms, the individuals said. OCE investigators have notified Bachus that he is under investigation and that they have found probable cause to believe insider-trading violations have occurred.

The case is the first of its kind involving a member of Congress. It comes at a time of intense public scrutiny of congressional ethics, with the House passing legislation Thursday to tighten rules against insider trading by lawmakers.