10 USC § 331. Federal aid for State governments
Whenever there is an insurrections in any State against its government, the President may, upon the request of its legislature or of its governor if the legislature cannot be convened, call into Federal service such of the militia of the other States, in the number requested by that State, and use such of the armed forces, as he considers necessary to suppress the insurrection.
(Aug. 10, 1956, ch. 1041, 70A Stat. 15.)