The subpoena for Matthew Parker, director of Ney's district office in St. Clairsville, Ohio, was issued by a federal magistrate in Washington and announced Thursday.
The subpoena news came as Roll Call reported that three of Ney's top aides had left or would soon be leaving, provoking questions about the state of the congressman's office.
In a statement, Ney advised against reading into the significance of the staff departures.
"As with every office on Capitol Hill, where staffers work very long hours, there is inevitably turnover," Ney said. "What is notable however, is that all three of the staff members who will soon be leaving my office all worked for me for much longer than the average tenure."
Ney has not been accused of wrongdoing, but federal prosecutors have described him in court documents as having received gifts, trips and other things of value from disgraced former lobbyist Jack Abramoff and his associates.
Ney's spokesman Brian Walsh declined to comment on Parker's subpoena.
Parker is the first member of Ney's staff to be subpoenaed by the Justice Department since Ney himself was subpoenaed in November. Ney's chief of staff, William Heaton, and Paul Vinovich, the staff lawyer for the House committee Ney used to lead, were subpoenaed by the defense in the related trial of former Bush administration official David Safavian, who was found guilty of lying and obstructing the federal corruption investigation.
Walsh said he will leave next month to take a job with Sen. John Cornyn, R-Texas. He also confirmed that Heaton, is leaving in July and Chris Otillio, Ney's former legislative director, left earlier this month.
Looking ahead to the November election, National Republican Congressional Committee communications director Carl Forti tells CBSNews.com that Ney has a "fully staffed campaign" and "staff turnover in his congressional office is irrelevant to his campaign" anyway.
Plus, Forti says, right now there is, above all else, speculation.
"Until something does happen, it's status quo," Forti explains.