A trade union (British English) or labor union (American English) is an organization of workers that have banded together to achieve common goals such as better working conditions. The trade union, through its leadership, bargains with the employer on behalf of union members (rank and file[1] members) and negotiates labour contracts (collective bargaining) with employers. This may include the negotiation of wages, work rules, complaint procedures, rules governing hiring, firing and promotion of workers, benefits, workplace safety and policies. The agreements negotiated by the union leaders are binding on the rank and file members and the employer and in some cases on other non-member workers.
Originating in Europe, trade unions became popular in many countries during the Industrial Revolution, when the lack of skill necessary to perform most jobs shifted employment bargaining power almost completely to the employers' side, causing many workers to be mistreated and underpaid. Trade union organizations may be composed of individual workers, professionals, past workers, or the unemployed. The most common, but by no means only, purpose of these organizations is "maintaining or improving the conditions of their employment".[2]
I see nothing in the definition of a trade Union about actively trying to reduce the rights of workers. A good TU should resist change, until a mutually agreed solution is negotiated. That is how it works. Unfortunately BA decided on the imposition route instead.