Hugo Black

“ Although the declaratory judgment sought by the plaintiffs was a statutory remedy rather than a traditional form of equitable relief, the Court made clear that a suit for declaratory judgment was nevertheless 'essentially an equitable cause of action,' and was 'analogous to the equity jurisdiction in suits quia timet or for a decree quieting title.' 319 U.S., at 300, 63 S.Ct., at 1074. ”

“ In our opinion in the Yougner case, we set out in detail the historical and practical basis for the settled doctrine of equity that a federal court should not enjoin a state criminal prosecution begun prior to the institution of the federal suit except in very unusual situations, where necessary to prevent immediate irreparable injury. The question presented here is whether under ordinary circumstances the same considerations that require the withholding of injunctive relief will make declaratory relief equally inappropriate. ”

“ It is also true that that procedure may in every practical sense operate to suspend collection of the state taxes until the litigation is ended. But we find it unnecessary to inquire whether the words of the statute may be so construed as to prohibit a declaration by federal courts concerning the invalidity of a state tax. ”