Washington (CNN) -- The Department of Homeland Security has more contractors working for it than full-time employees, a situation two members of Congress said Tuesday was "unacceptable, untenable and unsustainable."

Sen. Joseph Lieberman, the chairman of the Senate Homeland Security and Governmental Affairs Committee, and ranking Republican Susan Collins said they were "astounded" to learn there are more than 200,000 contractor employees at the department.

The civilian work force of Homeland Security numbers 188,000, according to an estimate provided to the senators by Homeland Security.

In a letter sent Tuesday to the agency's Secretary Janet Napolitano, Lieberman and Collins said the figure "raises the question of whether DHS itself is in charge of its programs and policies, or whether it inappropriately has ceded core decisions to contractors."