The Workers Party (WP)/Independent Socialist League (ISL), whose members were known as the Shachtmanites, obtained control of United Auto Workers (UAW) Local 6 through the dominant Positive Action Caucus (PAC). The Shachtmaniteled PAC red-baited the United Farm Equipment and Metal Workers Union (FE), the first time in U. S. trade union history in which a Marxist organization of the ostensibly revolutionary left aided in the destruction of a Communist Party USA-led union. Using Local 6 as the base from which to attack the FE, whose membership was concentrated in the Chicago-area Harvester plants, the PAC demonized Local 6's CPUSA-led caucus, the Committee to Build Local 6 (CBL6), by arguing that it was pro-CPUSA, pro-FE and anti-UAW. Once the PAC successfully painted the CBL6 as the adversary within the local possessing an ideology "foreign" to the UAW, it was easy to portray the FE as being the UAW's major enemy, which had to be destroyed at any cost.
Devinatz, Victor G., "A Cold War at international Harvester: The Shachtmanites and the farm equipment workers union's demise, 1946-1955" (2008). Faculty Publications-- Management and Quantitative Methods. Paper 2.