In Leedom v. Kyne (1958), the U.S. Supreme Court ruled that the National Labor Relations Board (NLRB) had overstepped its authority by including both professional and non-professional employees in a single bargaining unit without obtaining majority approval from the professionals, as required by Section 9(b)(1) of the National Labor Relations Act. The case arose when an NLRB-certified union included both types of workers, and a group of professional employees sued to invalidate this certification on grounds that they hadn't been given their right to vote separately on inclusion in such a unit. The Supreme Court agreed with them, stating that there was no other way for these professionals to protect their statutory rights except through judicial review.

In the dissenting opinion for Leedom v. Kyne, Justice Frankfurter argued that the majority's decision was an unwarranted intrusion into administrative law and a departure from established principles of judicial restraint. He contended that the National Labor Relations Board (NLRB) had acted within its authority when it certified a mixed bargaining unit of professional and non-professional employees without obtaining approval from the professionals as required by Section 9(b)(1) of the National Labor Relations Act. According to him, this issue should have been left to be resolved through collective bargaining or other internal union processes rather than court intervention. Furthermore, he pointed out that there were no allegations or evidence suggesting bad faith on part of NLRB in certifying such units; hence courts should not interfere with their decisions unless they are patently unlawful or made in bad faith.