WASHINGTON (AP) — Retiring Republican Rep. Steve Stockman of Texas and three of his aides say they have been subpoenaed by a federal grand jury in a criminal investigation.

Stockman notified Congress of the subpoena but did not reveal the nature of the federal investigation. Stockman lost a primary election for Senate and is retiring after two terms representing the Houston area.

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, Jason Posey and Thomas Dodd, have since been fired, Stockman's office said earlier this year when the ethics investigation became public.

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

A spokesman for the Justice Department declined to comment.

In June, the independent Office of Congressional Ethics found "substantial reason" to believe Stockman broke campaign finance laws and House ethics rules. The ethics office also said it had reason to believe Stockman "made false statements and endeavored to impede" its inquiry. The ethics office is an independent agency that refers cases to the House Ethics Committee.

Stockman has acknowledged making "reporting errors" on campaign finance reports, but has said they were later corrected. He also has said he is cooperating with the ethics panel.

Besides Stockman, three aides submitted statements saying they have been subpoenaed: senior communications and policy adviser Donny Ferguson, legislative assistant Prentice Leblanc and executive assistant Kristine Brakstad.

Ferguson, who serves as Stockman's chief spokesman, could not be reached for comment.

Sen. John Cornyn, R-Texas, trounced Stockman in a primary this spring. Stockman, who also served one term in the House in the 1990s, did not seek re-election to the House.