Producer Cooperative - nonprofit association of producers helping members sell or market products. In the US., most coops of this kind are made up of farmers. The coop helps the farmers sell their crops directly to central markets or to companies that use the members' products. Any savings that the producer coop makes in marketing costs go to its members. Professional Association - nonprofit association of professional or specialized workers seeking to improve working conditions, skill levels, and public perceptions of it profession.
Membership can be either mandatory or voluntary.
Examples include The American Association of University Professors and the American Bar Association. The government watches trade associations rather carefully so that they do not violate collusion and anti trust laws. NAM members include any US corporation that manufacturers anything. This is a HUGE organization. Members include General Motors, IBM, Caterpillar, etc.