Labor union
A labor union or trade union is an organization formed for the purpose of collectively representing the interests of a group of workers. In particular this can include collectively bargaining with employers in order to agree rates of pay and other conditions of employment. Conservatives tolerate the right of workers to form unions but recoil when they become too liberal, too corrupt, or too authoritarian over their members. Liberals aggressively support them, and use their influence with labor leaders to force rank-and-file union members to support liberal causes and candidates financially, despite the fact that those members strongly and unequivocally oppose those causes and candidates.
In most countries unions are on the left politically.