Washington (CNN) The Interior Department's Inspector General has opened an investigation into potential ethics violations of several senior executives at the department, according to a letter obtained by CNN.

The inspector general opened the investigation after the Campaign Legal Center, a nonpartisan ethics group, submitted a complaint to the office in February. The complaint named six senior executives in the department who continued to do some work or meet with people the executives for whom they had previously lobbied or worked.

The complaint highlighted potential ethics violations from Interior employees in leadership positions including the department's Deputy Director of Intergovernmental and External Affairs Benjamin Cassidy, White House Liaison Lori Mashburn and Deputy Director of Intergovernmental and External Affairs Timothy Williams. All six named in the complaint are political appointees.

The complaint details instances where these officials met with people who worked for their previous employers while they were working in their roles at Interior. In Cassidy's case, the complaint says that he continued to meet with and solicited comments from National Rifle Association officials about Interior plans that would impact the NRA. Cassidy lobbied for the NRA before working at Interior.

Assistant Secretary for Insular and International Affairs Doug Domenech was the director for the fueling freedom project at the Texas Public Policy Foundation before joining the department. The complaint alleges that Domenech met privately with his former employer to discuss an ongoing lawsuit between the department and foundation. Six months later, Interior settled the lawsuit, according to the complaint.

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