Whether the Court should apply ordinary gender-based equal-protection scrutiny without special regard for Congress's military judgments, or instead apply rational-basis review because the statute concerns national defense.
Holding
The Court declined to adopt a separate, formulaic level of scrutiny for this setting, but held that substantial judicial deference is due to Congress's considered judgments when it acts under its express constitutional authority to raise and regulate the armed forces.
Reasoning
The Fifth Amendment's Due Process Clause incorporates an equal-protection constraint against unjustifiable federal discrimination, and Congress does not escape constitutional limits merely because it acts in the military sphere. But Congress's Article I authority to raise and support armies and regulate the land and naval forces is broad, while courts lack institutional competence to second-guess professional judgments about force composition, training, mobilization, and military readiness.
Registration could not be separated from military affairs simply because registrants were civilians. Registration was the first step toward induction and had no independent civilian purpose. Therefore, the constitutionality of the registration system necessarily depended on Congress's judgments about the personnel needed in a future draft.
The Court rejected the Government's invitation to reduce review to rational-basis scrutiny, but also rejected a mechanical application of doctrinal labels. The relevant inquiry was whether Congress's studied choice between male-only registration and registration of both sexes denied equal protection, while giving appropriate weight to Congress's constitutionally assigned responsibility for national defense.