A group of workers who organize to advance and protect their own interests is called:

A) a union
B) a professional association
C) a team
D) a collectivity
E) a solidary group

A union is a specific type of group that is organized for the purpose of protecting workers' interests, such as negotiating for better wages and working conditions. Professional associations and teams may also exist to advance the interests of members, but they do not necessarily involve collective bargaining or other forms of direct action. Collectivities and solidary groups are more general terms that refer to any group of people who share common goals or interests.