Between 1931 and 1936 UE formed independently of the American Federation of Labor (AFL) and other established craft unions. The primary figures in UE's leadership were General-President Albert J. Fitzgerald, Secretary-General Julis Emspak and the Director of Organization James J. Matles. UE functioned under the newly formed Congress of Industrial Organizations (CIO). UE was the first union chartered in a mass production industry outside the AFL. In 1937 UE changed its name from United Electrical and Radio Workers of America to United Electrical, Radio and Machine Workers of America. By an act of the UE International convention, Local 1412 was chartered on June 3, 1938 to "organize the unorganized" in the Bay Area. Local 1412 adopted its Constitution and By-laws on October 28, 1949. Headquartered in Oakland, California, Local 1412 "collectively pursued an aggressive struggle" to protect its members and shops from the organized forces of the employers.

By 1943 UE had become the third largest of all CIO unions ranking behind the auto and steel worker unions. In 1946 these three unions collectively fought for a $2.00 a day increase in wages based on the fact that from 1940 to 1945 the cost of living increased 45% and the wages only rose 15% while corporations posted a net profit of 117 billion dollars for this period. UE waged a national strike against General Electric and Westinghouse. Eventually the strike was settled with UE obtaining an 18% increase in wages for all its members, men and women.

The major industrial corporations were threatened by what they perceived to be the militant unity of the CIO. These corporations collectively pressured the Federal Government to act. The Taft-Hartley bill was legislation aimed at halting union organization of unskilled workers in mass production industries. Passed in 1947, its purpose was to fragment the industrial union movement. It attempted to weaken the active shop steward system through encouraging workers to bypass the shop steward and take up their own individual grievances with management. It also encouraged the breakaway of craftsmen and professional workers from industrial unions. Most importantly the bill made union members sign "noncommunist affidavits." If a union refused to sign an affidavit it could not use the facilities of the National Labor Relations' Board (NLRB) or cast ballots in labor board elections, and its individuals would be expelled from the union.

Most of the unions in the CIO decided to comply with the Taft-Hartley bill. However, UE, the West Coast Longshoremen and a handful of other unions refused to sign the noncommunist affidavits. This led to UE's subsequent break with the CIO in 1948. UE's refusal to expel any member for a political belief led to a barrage of attacks from the CIO, General Electric, Westinghouse and the Federal Government. Their assaults took the form of slanderous redbaiting campaigns in local shop elections, the refusal from General Electric and Westinghouse to recognize UE as a union, and an endless series of Congressional-sponsored investigations. During the 1950s and early 1960s UE was investigated by a host of Senate committees on "un-American activities," starting with the McCarthy committee, then progressing through the Eastland, Butler and Kerstein committees and ending with an investigation by the Subversive Activities Control Board. Throughout this period UE suffered great losses in credibility and membership. In 1955 UE had 140,000 members and this number had increased steadily until 1986 when UE boasted over 160,000 members.

In 1969 UE and the International Union of Electrical and Radio Workers, AFL-CIO combined forces in a national strike and negotiation effort against General Electric and Westinghouse. They effectively fought for improved working conditions and protected workers against layoffs due to automation or plant closings. They countered GE's post-war practice of shifting plants overseas or to low-wage areas of this country. Also UE ended General Electric's tradition of avoiding the equal-pay-for-equal-work standard by classifying certain jobs, mostly performed by women, at rates which might be lower than unskilled rates for cleanup or sweeper jobs.