Here is that opinion: LRB v. NLRB

An excerpt:

Plaintiff has simply not established federal-question jurisdiction. The NLRA does not create a cause of action for a plaintiff in federal district court. To the extent plaintiff’s right to relief depends on resolution of a substantial question of federal law, namely, the NLRB’s exercise of jurisdiction over it, that question is properly decided by the NLRA in the first instance, then the court of appeals. This Court lacks jurisdiction to prevent the NLRB from proceeding on the charge that plaintiff is engaged in an unfair labor practice.

Briefs and other materials here and here.