The 1976 Arms Export Control Act requires the president to notify Congress of any arms sale greater than $14 million, and it empowers Congress to block or modify an arms sale at any point before delivery by adopting a “resolution of disapproval.”

Because the law prevents senators from filibustering the disapproval resolution, the Senate can adopt it by a simple majority vote. But the law also allows the president to veto the resolution. To block an arms sale, congressional opponents need a two-thirds majority in both chambers to override a president’s veto.

Members of Congress have tried in the past to pass objections to proposed arms sales. That succeeded only once, in 1986, when a Republican Senate and a Democratic House voted to block the proposed sale of Sidewinder, Harpoon and Stinger missiles to Saudi Arabia. Although President Ronald Reagan vetoed the resolution, congressional opposition led the administration to alter the deal. Saudi Arabia ultimately received only Sidewinder and Harpoon missiles. Other congressional attempts to block arms sales proposed by the president have failed.