A Texas congressman and three of his aides say they have been subpoenaed by a federal grand jury in a criminal investigation.

Republican Rep. Steve Stockman of Texas lost a primary election for Senate and is retiring. He notified Congress of the subpoena but did not reveal the nature of the federal investigation. Stockman did not seek re-election to the House.

The House Ethics Committee has been investigating allegations that Stockman accepted campaign contributions from two staffers and falsified payroll records to hide the contributions. The staff members have since been fired.

Stockman and three aides submitted formal statements to the House clerk acknowledging the subpoenas and declaring that they are complying with them.

Stockman has said he is cooperating with the ethics panel.