Democratic Sen. Tammy Duckworth wrote that she fears “repeated tacit threats” could be weakening the Department of Homeland Security inspector general’s independence.

The Department of Homeland Security’s general counsel warned the agency’s independent watchdog that DHS Secretary Kristi Noem asserts that she has the power to unilaterally kill their investigations, according to a new letter sent by Illinois Democratic Sen. Tammy Duckworth to Noem.

The DHS inspector general’s office states that its mission is to “provide objective, independent oversight of DHS programs and operations and to promote excellence, integrity, and accountability within DHS.”

In a meeting with DHS Inspector General Joseph Cuffari, Duckworth learned that DHS general counsel communicated multiple times with DHS OIG to “remind them” that Noem has the power to kill investigations by his department, according to the letter obtained by NBC News.

Duckworth says she also learned the IG’s office was also asked on Jan. 29 to disclose “every active audit, inspection and criminal investigation,” which the lawmaker writes is “extremely unusual, perhaps even unprecedented.”