1.1503-1—Computation and payment of tax.
(a) General rule.
In any case in which a consolidated return is filed or required to be filed, the tax shall be determined, computed, assessed, collected, and adjusted in accordance with the regulations prescribed under section 1502 promulgated prior to the last date prescribed by law for the filing of such return.
(b) Limitation.
If the affiliated group includes one or more Western Hemisphere trade corporations (as defined in section 921) or one or more regulated public utilities (as defined in section 1503 (c) ), the increase in tax described in section 1503 (a) shall be applied in a manner provided in the regulations under section 1502.