Government has reserved unto itself to decide when, if and how much its pay raise shall be. Pretty sweet deal. They grant themselves all kinds of nice perks, too. Often, lifetime perks. Until recently, any Congressman or Senator could keep for themselves upon leaving the Congress any unused campaign contributions they had raised over the years. Don't know if this policy has changed, but many left office with millions of dollars converted from old campaign funds.
A humorist once said Congress is America's only permanent criminal class.