Federal employees wages and benefits are set by Congress.

From WSJ Op/Ed:

"In 1978, Democratic President Jimmy Carter, backed by a Democratic Congress, passed the Civil Service Reform Act. Washington had already established its General Schedule (GS) classification and pay system for workers. The 1978 bill went further, focused as it was on worker accountability and performance. It severely proscribed the issues over which employees could bargain, as well as prohibited compulsory union support. "

WSJ Op/Ed