Sen. Richard Shelby (R-Ala.) is on the Senate floor now introducing a bill that would amend the U.S. Constitution to require a balanced budget except in certain circumstances.

Shelby said Tuesday that his proposal would require the U.S. to spend only the amount is receives in revenues, except in times of war or when three-fifths of the House and Senate vote to spend more. Sen. Mark Udall (D-Colo.) also spoke in support of the bill.