Justice Department investigators have issued subpoenas to Nevada businesses, seeking information related to Sen. John Ensign (R-Nev.) and his former aide Doug Hampton, CBS affiliate KLAS-TV reported Wednesday.

Both the Senate Ethics Committee and the FBI are investigating Ensign’s involvement in procuring lobbying work for Hampton after Ensign ended an affair with Hampton’s wife, Cynthia Hampton. A $96,000 payment that Ensign’s parents made to the Hamptons may also be under review.

The KLAS-TV Web site reports that at least six Las Vegas-area businesses received subpoenas March 8, served by an FBI agent and a prosecutor from DOJ’s Public Integrity Section.

According to a redacted copy of one subpoena, the DOJ is also seeking any documents — including calendars, e-mails, photographs, notes, memoranda and other items — that mention Ensign or the Hamptons, as well as former Ensign Chief of Staff John Lopez and any contacts with Ensign’s staff.

The subpoenas also seek any documents that reference Michael and Lindsey Slanker. Michael Slanker, a former Ensign political lieutenant, is the founder of November Inc., a lobbying firm that hired Hampton after he left Ensign’s office. Ensign is reported to have coordinated Hampton’s move to the firm and helped him secure clients including Allegiant Air and NV Energy.

Michael Slanker has also managed Ensign’s Senate bids and served as the National Republican Senatorial Committee’s political director under Ensign during the 2008 election cycle. His wife, Lindsey, has served as the NRSC’s finance director.

In addition, the subpoenas require the disclosure of any documents that refer post-employment restrictions for Senate aides. If Ensign did help his one-time top aide secure lobbying clients, it would potentially violate the Senate’s one-year revolving-door ban.

The redacted subpoenas indicate all materials must be submitted by March 31, the scheduled day for testimony at the U.S. District Court for the District of Columbia.