Unions and employers have also employed arbitration to resolve employee and union grievances arising under a collective bargaining agreement. The Amalgamated Clothing Workers of America made arbitration a central element of the "Protocol of Peace" it negotiated with garment manufacturers in the second decade of the twentieth century. Grievance arbitration became even more popular during World War II, when most unions had adopted a no-strike pledge. The War Labor Board, which attempted to mediate disputes over contract terms, pressed for inclusion of grievance arbitration in collective bargaining agreements. The Supreme Court subsequently made labor arbitration a key aspect of federal labor policy in three cases which came to be known as the Steelworkers' Trilogy. The Court held that grievance arbitration was a preferred dispute resolution technique and that courts could not overturn arbitrators' awards unless the award does not draw its essence from the collective bargaining agreement. State and federal statutes may allow vacating an award on narrow grounds ("e.g.", fraud). These protections for arbitrator awards are premised on the union-management system, which provides both parties with due process. Due process in this context means that both parties have experienced representation throughout the process, and that the arbitrators practice only as neutrals. "See" National Academy of Arbitrators.