Atlantic Coast Line Railroad Co. v. Brotherhood of Locomotive Engineers
In Atlantic Coast Line Railroad Co. v. Brotherhood of Locomotive Engineers, 398 U.S. 281, 286-87, 90 S.Ct. 1739, 1742-43, 26 L.Ed.2d 234 (1970), the Court ruled that, despite the obviously strong federal interest in labor relations, the federal courts are prohibited from enjoining state court proceedings unless that action can "be justified by any of the three exceptions."
As the Court explained:
In 1955 when this Court interpreted this statute, it stated: "This is not a statute conveying a broad general policy for appropriate ad hoc application. Legislative policy is here expressed in a clear-cut prohibition qualified only by specifically defined exceptions." Amalgamated Clothing Workers v. Richman Bros., 348 U.S. 511, 515-16 75 S.Ct. 452, 455-56, 99 L.Ed. 600 (1955). Since that time Congress has not seen fit to amend the statute and we therefore adhere to that position and hold that any injunction against state court proceedings otherwise proper under general equitable principles must be based on one of the specific statutory exceptions to Sec. 2283 if it is to be upheld. Moreover since the statutory prohibition against such injunctions in part rests on the fundamental constitutional independence of the States and their courts, the exceptions should not be enlarged by loose statutory construction. Proceedings in state courts should normally be allowed to continue unimpaired by intervention of the lower federal courts, with relief from error, if any, through the state appellate courts and ultimately this Court. (Id. at 287, 90 S.Ct. at 1743.)