In many countries, a union may acquire the status of a legal entity, with a mandate to negotiate with employers for the workers it represents. In such cases, unions have certain legal rights, most importantly the right to negotiate collectively with the employer (or employers) over wages, working hours and other terms and conditions of employment. The inability of both parties to reach an agreement may lead to industrial action, culminating in either strike action or management lockout. In extreme cases, violent or illegal activities may develop around these events.
In other circumstances, unions may not have the legal right to represent workers, or the right may be in question. This lack of status can range from non-recognition of a union to political or criminal prosecution of union activists and members, with many cases of violence and deaths having been recorded both historically and in the current day.
Unions may also engage in broader political or social struggle. Social Unionism encompasses many unions which use their organisational strength to advocate for social policies and legislation favourable to their members or to workers in general. As well, unions in some countries are closely aligned with political parties.
Unions are also delineated by the service model and the organising model. The service model union focuses more on maintaining worker rights, providing services, and resolving disputes. Alternately, the organising model typically involves full-time organisers, who work by building up confidence, strong networks and leaders within the workforce; and confrontational campaigns involving large numbers of union members. Many unions are a blend of these two philosophies, and the definitions of the models themselves are still debated.
Although their political structure and autonomy varies widely, union leaderships are usually formed through democratic elections.
Some research, such as that conducted by the Australian Centre for Industrial Relations Research and Training (ACIRRT), argues that unionised workers enjoy better conditions and wages than those who are not unionised.