pressure group

group which works for a specific cause, lobbyists

An interest group (also called an advocacy group, lobbying group, pressure group (UK), or special interest) is a group, however loosely or tightly organized, doing advocacy: those determined to encourage or prevent changes in public policy without trying to be elected.
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Noun
1. a group of people who try actively to influence legislation
(synonym) lobby, third house
(hypernym) political unit
(hyponym) National Rifle Association, NRA

any group of individuals who work together to exert an influence upon the decision-making of a company to achieve some specific outcome.

See entry under interest group .