Well, Darkcat left a great link in the comments section-here are a few key pieces:
ROSTKER V. GOLDBERG, 453 U. S. 57 (1981)
The Military Selective Service Act (Act) authorizes the President to require the registration for possible military service of males, but not females, the purpose of registration being to facilitate any eventual conscription under the Act. Registration for the draft was discontinued by Presidential Proclamation in 1975 (the Act was amended in 1973 to preclude conscription), but as the result of a crisis in Southwestern Asia, President Carter decided in 1980 that it was necessary to reactivate the registration process, and sought Congress’ allocation of funds for that purpose. He also recommended that Congress amend the Act to permit the registration and conscription of women as well as men. Although agreeing that it was necessary to reactivate the registration process, Congress allocated only those funds necessary to register males, and declined to amend the Act to permit the registration of women. Thereafter, the President ordered the registration of specified groups of young men. In a lawsuit brought by several men challenging the Act’s constitutionality, a three-judge District Court ultimately held that the Act’s gender-based discrimination violated the Due Process Clause of the Fifth Amendment, and enjoined registration under the Act.
Held: The Act’s registration provisions do not violate the Fifth Amendment. Congress acted well within its constitutional authority to raise and regulate armies and navies when it authorized the registration of men and not women. Pp. 453 U. S. 64-83.
H.J.Res. 521 only authorized funds sufficient to cover the registration of males. The Report of the Senate Committee on Appropriations on H.J.Res. 521 noted that the amount authorized was below the President’s request “due to the Committee’s decision not to provide $8,500,000 to register women,” and that “[t]he amount recommended by the Committee would allow for registration of young men only.” S.Rep. No. 9789, p. 2 (1980); see 126 Cong.Rec. 13895 (1980) (Sen. Nunn).
“Registering women for assignment to combat or assigning women to combat positions in peacetime then would leave the actual performance of sexually mixed units as an experiment to be conducted in war with unknown risk — a risk that the committee finds militarily unwarranted and dangerous. Moreover, the committee feels that any attempt to assign women to combat positions could affect the national resolve at the time of mobilization, a time of great strain on all aspects of the Nation’s resources.”
END SELECTIVE SERVICE NOW!!!!