Retiring U.S. Rep. Steve Stockman and three of his Capitol Hill aides notified Congress on Wednesday that they have been subpoenaed by a federal grand jury in an ongoing criminal investigation.

Stockman, a Clear Lake Republican who lost a primary election for U.S. Senate this year, did not divulge the nature of the federal probe.

The House Ethics Committee has been looking into allegations of illegal campaign contributions and falsified payroll records brought to light by watchdog groups, the Houston Chronicle and congressional investigators.

In a formal statement read by a clerk on the House floor, Stockman acknowledged the subpoenas and said he was conferring with his lawyers to determine whether compliance would be “consistent with the privileges and rights of the House.”

Statements by three of his aides followed: senior communications and policy adviser Donny Ferguson, legislative assistant Prentice Leblanc and executive assistant Kristine Brakstad.

All three aides indicated they would cooperate with the subpoenas, which were issued by the U.S. District Court for the District of Columbia.

Ferguson, who acts as Stockman’s spokesman, did not return calls and emails seeking comment.