Congress is required by Article I, Section 6, of the Constitution to determine its own pay.
Pay adjustments can be enacted through stand-alone legislation or through a commission process, but most commonly member salary increases are implemented through an automatic annual adjustment process in which members receive an automatic “cost of living” allowance increase.
The salary increase takes effect on January 1 of each year unless Congress votes to decline it, though individual members can opt to decline an automatic annual pay increase. By law, members may not receive an increase greater than the increase in the base pay of General Schedule (GS) employees. Both houses of Congress voted not to raise member salaries for 2010 or 2011.