The following is the April 2, 2019 Congressional Research Service report, Arms Sales: Congressional Review Process.

From the report

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 retransfer to third-party states of such military items. Under Section 36(b) of 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, South Korea, Israel, or New Zealand, Congress must be formally notified 15 calendar days before the Administration can proceed with the sale. However, the prior notice threshold values are higher for sales to NATO members, Japan, Australia, South Korea, Israel, or New Zealand. Commercially licensed arms sales also must be formally notified to Congress 30 calendar days before the export license is issued if they involve the sale of major defense equipment valued at $14 million or more, or defense articles or services valued at $50 million or more (Section 36(c) AECA). In the case of such sales to NATO member states, NATO, Japan, Australia, South Korea, Israel, or New Zealand, Congress must be formally notified 15 calendar days before the Administration is authorized to proceed with a given sale. As with government-to-government sales, the prior notice threshold values are higher for sales to NATO members, Japan, Australia, South Korea, Israel, or New Zealand.

Furthermore, commercially licensed arms sales cases involving defense articles that are firearms-controlled under category I of the United States Munitions List and valued at $1 million or more must also be formally notified to Congress for review 30 days prior to the license for export being approved. In the case of proposed licenses for such sales to NATO members, Japan, Australia, South Korea, Israel, or New Zealand, 15 days prior notification is required.

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 faces 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. This report will be updated, if notable changes in these review procedures or applicable law occur.

Download the document here.