Local 192 of the Amalgamated Transit Union (ATU), the first ATU local in California, was founded in Oakland in 1901. The Local 192's parent union, the international ATU, is today the largest transit workers' union in North America, including 273 locals in the US and Canada.

The history of Local 192 is intertwined with its bargaining counterparts: Key System Transit, AC Transit, and Bay Area Rapid Transit (BART). Key System Transit, which existed between 1903 and 1960, was a privately owned mass transit company that operated streetcar and bus lines in the East Bay. In addition, Key System operated commuter rail and bus lines to San Francisco via bay ferries and the Bay Bridge. Facing bankruptcy by declining ridership in the wake of the ascendance of the automobile and the targeted campaign of General Motors to destroy public transit systems , local streetcar service in the East Bay ended in 1948 and service to San Francisco ceased in 1958.

After this, AC Transit, a public transit system, took over much of the old Key System. AC Transit has its origins in a 1956 vote by East Bay citizens to form the publicly owned and operated Alameda Contra Costa Transit District, approving a bond of $16.5 million that allowed AC Transit to acquire the bankrupt Key System from the California Public Utilities Commission in 1960. Thus, ATU 192 became the bargaining representative for the employees of the AC Transit District; a bargaining relationship that still exists today.

For a time, ATU 192 also represented workers at Bay Area Rapid Transit District (BART). Public employers had not been covered by the National Labor Relations Act of 1935, which affirmed the legal right of most American workers to form labor unions and set up the National Labor Relations Board to oversee union elections and arbitrate disputes and grievances. By the time of BART's formation, Section 13 (C ) of the 1964 Urban Mass Transportation Act required local transit union approval on federally funded transit projects, guaranteeing collective bargaining for workers in systems like BART. ATU 192 argued that their members should be allowed to "follow their work" onto the new system with all their union representation, seniority, contract wages and pension benefits intact, negotiating such an agreement with BART and other unions in the Bay Area in 1968.The unions improved their position by negotiating an interim preferential hiring agreement in early 1968.

Under this agreement, transit employees of existing systems would be given notice and have the first chance at jobs. However, BART had already hired non-transit office and technical employees. The Service Employees International Union (SEIU), claimed a right to organize this group of unorganized workers.

A conflict ensued about which union should be the representative of BART employees between 1968 and 1972, when an arbitrator's award under the Section 13 (C) agreement finally articulated the priority for filling BART jobs. Over a thousand employees of existing systems made applications under the terms of the arbitrator's award, but by late 1973, only 73 of almost 600 eligible ATU employees worked at BART. At this point, the SEIU threatened a strike if the priority hiring and recognition of seniority under the arbitrator's award impacted the members it was organizing. ATU 192 and 15 other unions were forced into representation elections for the BART system.

The ATU gained a partial victory through effective organizing, winning the operating sub-unit of five separate units and establishing ATU Local 1555 to represent its members at BART. As a result, the SEIU won the right to represent maintenance and clerical employees. Thus, ATU 192's relationship with BART ended except for multi-party arbitrations regarding the right to represent workers on BART-affiliated bus lines. As of 2008, Local 192 represents 1,400 members, including workers in AC Transit.