"This report reviews the process and procedures that currently apply to congressional consideration of foreign arms sales proposed by the President. This includes consideration of proposals to sell major defense equipment, defense articles and services, or the re-transfer to third party nations of such military items. Under […] the Arms Export Control Act (AECA), Congress must be formally notified 30 calendar days before the Administration can take the final steps to conclude a government-to-government foreign military sale of major defense equipment valued at $14 million or more, defense articles or services valued at $50 million or more, or design and construction services valued at $200 million or more. In the case of such sales to NATO member states, NATO, Japan, Australia, or New Zealand, Congress must be formally notified 15 calendar days before the Administration can proceed with the sale. […]. In general, the executive branch, after complying with the terms of applicable U.S. law, principally contained in the AECA, is free to proceed with an arms sales proposal unless Congress passes legislation prohibiting or modifying the proposed sale. Under current law Congress must overcome two fundamental obstacles to block or modify a Presidential sale of military equipment: it must pass legislation expressing its will on the sale, and it must be capable of overriding a presumptive Presidential veto of such legislation. Congress, however, is free to pass legislation to block or modify an arms sale at any time up to the point of delivery of the items involved."
CRS Report for Congress, RL31675