What is the purpose of a Political Action Committee (PAC)? A PAC is the political arm of an interest group, and it funnels money to candidates that support its cause. A PAC is an interest group whose job is to lobby members of Congress to support certain causes. A PAC is an alternative to a political interest group for those who oppose traditional lobbying. A PAC is a business interest group that works to get members of Congress to vote pro-business.