War Powers Resolution

The War Powers Resolution (also known as the War Powers Resolution of 1973 or the War Powers Act) (50 U.S.C. 1541–1548) is a federal law planned to check the U.S. president's power to commit the United States to an armed conflict without the approval of the U.S. Congress. 
The resolution was adopted in the form of a United States congressional joint resolution. It says that the president can send the U.S. Armed Forces into action abroad only by declaration of war by Congress.