From Networkip, LLC v. FCC, 548 F.3d 116 (D.C. Cir. 2008):
Though agencies are entitled to deference, they may not retroactively change the rules at will. Indeed, that "[e]lementary considerations of fairness dictate that individuals should have an opportunity to know what the law is and to conform their conduct accordingly" has been well ...
From Networkip, LLC v. FCC, 548 F.3d 116 (D.C. Cir. 2008):
Though agencies are entitled to deference, they may not retroactively change the rules at will. Indeed, that “[e]lementary considerations of fairness dictate that individuals should have an opportunity to…