The State Department's  inspector general will look in to the program that allowed a top aide to Hillary Clinton to simultaneously work for the department and a private sector consulting firm, officials said Friday.

Inspector General Steve Linick wrote in a letter to Sen. Charles Grassley (R-Iowa) Thursday informing him of the preliminary inquiry into the operation of the Special Government Employee Program at State. Grassley had asked Linick to look in to the use of the program by Huma Abedin, a top personal aide to Clinton, who now directs the former secretary of state's personal office in New York City.

"This program is meant to be used in a limited way to give the government special expertise it can't get otherwise," said Grassley, who chairs the Senate Judiciary Committee, in a statement released Friday afternoon. "Is the program working the way it's intended at the State Department or has it been turned on its head?"

Word of the inquiry comes as Clinton is preparing to formally launch her 2016 presidential campaign on Sunday. A spokesman for Hillary Clinton and Abedin did not respond to a request for comment.

Since 2013, Grassley has expressed concern about possible conflicts of interest that could arise by use of the program. He has focused on special employment grants to those who might be considered personal or political aides to Clinton while she was at State.

Abedin retained a State Department position after moving to New York to join her husband, former Democratic congressman Anthony Weiner, and take up part-time work in the private sector.  One of her employers was an international consulting firm, Teneo, that was founded by former Clinton associates.

Grassley asked State and 13 other federal agencies to outline their use of the program. At State, Grassley asked for all communication between the department and Teneo. The department did not respond to his request, which he reiterated last month amid reports that Clinton and Abedin had used a private e-mail server for State Department business.