IN THREE significant cases decided last term, the Supreme Court considered for the first time an old and slippery problem-the proper judicial approach to disputes concerning the jurisdiction of arbitrators under collective bargaining agreements. These cases arose under Section 301 of the LMRA,1 which in Lincoln Mills2 had been interpreted as a mandate to federal courts to give specific enforcement to agreements for grievance-arbitration and to fashion a body of substantive law for all actions under that section for breach of labor agreements. In two of the cases,3 the union had sought to compel arbitration by an unwilling employer; in the third,4 enforcement of an arbitration award. In each of the cases, the Court, reversing the judgment below, sustained the arbitrator's competence.5 The Court used these cases as