Cammer began practicing law with the firm of Boudin & Wittenberg from 1932 to 1933, and Zalkin & Cohen from 1933 to 1936.
In 1936, he joined his long-time friend Lee Pressman in the firm of Liebman, Robbins, Pressman & Leider, and stayed with the firm until 1941.
After his friend, Nathan Witt, resigned from the National Labor Relations Board following accusations in December 1940 that he was a member of the Communist Party (CPUSA), Cammer formed the law firm of Witt & Cammer in 1941.

Client included:  the Congress of Industrial Organizations (CIO); the Joint Board, Fur, Leather & Machine Workers Union; the Brewery Workers' Union (now International Union of United Brewery, Flour, Cereal, Soft Drink and Distillery Workers, New York Teachers Union, and Amalgamated Meat Cutters union.
Cammer began practicing law with the firm of Boudin & Wittenberg from 1932 to 1933, and Zalkin & Cohen from 1933 to 1936. In 1936, he joined his long-time friend Lee Pressman in the firm of Liebman, Robbins, Pressman & Leider, and stayed with the firm until 1941. After his friend, Nathan Witt, resigned from the National Labor Relations Board following accusations in December 1940 that he was a member of the Communist Party (CPUSA), Cammer formed the law firm of Witt & Cammer in 1941.
Client included:  the Congress of Industrial Organizations (CIO); the Joint Board, Fur, Leather & Machine Workers Union; the Brewery Workers' Union (now International Union of United Brewery, Flour, Cereal, Soft Drink and Distillery Workers, New York Teachers Union, and Amalgamated Meat Cutters union.
Harold I. Cammer