The Third Circuit has held that a state law claim relates to an employee benefit plan if "the existence of an ERISA plan [is] a critical factor in establishing liability" and "the trial court's inquiry would be directed to the plan."

—holding that injunction against prosecution of state court contract action brought by laid off employees against employer did not come within exception in the Anti-Injunction Act as "expressly authorized by Act of Congress" simply because the state-court claims were preempted by ERISA, even if the state court claims were subject to exclusive federal jurisdiction

A state law cause of action "relates to" an employee benefits plan if, without the plan, there would be no cause of action.

Id. "[T] he typical application of this exception has been in removal cases (where a district court must ensure its exclusive governance of the particular litigation removed) and in in rem cases (where, under the traditional view, only one court can entertain jurisdiction over a particular physical res)."

—concluding that a federal injunction of ongoing state proceedings in a case that has been removed to federal court falls within the first or third exception to the Anti-Injunction Act

Instead, the Court asks whether "the existence of an ERISA plan [is] a critical factor" in the plaintiff's legal claims.

The Supreme Court has described the test for whether a statute "expressly" [4] authorizes an exception to the Anti-Injunction Act as whether an Act of Congress, clearly creating a federal right or remedy enforceable in a federal court of equity, could be given its intended scope only by the stay of a state court proceeding.

Because this Court's "inquiry would be directed to the plan," the unjust enrichment claim "relates to" an ERISA plan and is preempted.

Courts considering the question have unanimously held that a plaintiff's fraudulent attempt to subvert the removal statute implicates the "expressly authorized" exception to the Anti-Injunction Act and may warrant the granting of an anti-suit injunction.