Except as provided in section 3803(c) of this title, nothing contained in this chapter shall be construed to repeal, amend, or suspend the laws now in force authorizing voluntary enlistment or reenlistment in the Armed Forces of the United States, including the reserve components thereof, except that no person shall be accepted for enlistment after he has been issued an order to report for induction unless authorized by the Director and the Secretary of Defense and except that, whenever the Congress or the President has declared that the national interest is imperiled, voluntary enlistment or reenlistment in such forces, and their reserve components, may be suspended by the President to such extent as he may deem necessary in the interest of national defense.