The National War Labor Board was instrumental in institutionalizing and legitimating unions in the United States because it provided a legal forum that recognized the role of unions in representing worker needs.

The National War Labor Board played a significant role in recognizing and promoting the importance of unions in representing worker needs. It helped establish collective bargaining between employers and unions, regulated labor disputes, and set standards for wages and working conditions. Through its actions, it helped foster an environment in which unions could thrive and gain legitimacy as important representatives of workers' interests.