Wadley Southern Railway Company v…
“ A statute, therefore, which imposes heavy penalties for violation of commands of an unascertained quality is, in its nature, somewhat akin to an ex post facto law, since it punishes for an act done when the legality of the command has not been authoritatively determined. Liability to a penalty for violation of such orders, before their validity has been determined, would put the part affected in a position where he himself must, at his own risk, pass upon the question. He must either obey what may finally be held to be a void order, or disobey what may ultimately be held to be a lawful order. ”
