(CNN) Key Democratic lawmakers are calling on the State Department's watchdog to conduct an "immediate review" of personnel practices after a number of employees told CNN they were unlawfully targeted for political reasons due to their work under the last administration.

The employees had been reassigned from their areas of expertise to help clear the backlog of Freedom of Information Act requests, which Secretary of State Rex Tillerson has designated as a priority. The employees regarded the move as retaliation.

"Our staffs have been made aware of credible allegations that the State Department has required high-level career civil servants, with distinguished records, serving administrations of both parties, to move to performing tasks outside their area of substantive expertise," Reps. Eliot Engel, the top Democrat on the House Foreign Affairs Committee, and Elijah Cummings, the top Democrat on the House Oversight Committee, wrote in a letter to the State Department's Inspector General sent Friday.

"At the very least, this is a waste of taxpayer dollars. At worst it may constitute impermissible abuse and retaliation," the letter read.

The letter to the inspector general cites a CNN report Friday that a growing number of State Department employees say they are being put in career purgatory because of their previous work on policy priorities associated with President Barack Obama and in offices the Trump administration is interested in closing.

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