SAN FRANCISCO — A group of professional golf caddies have taken aim at the PGA Tour in a class action claiming the organization forces them to serve as walking billboards without compensation.

The caddies say PGA Tour Inc. violated federal antitrust law by making them wear colorful bibs that display advertisements for tournament sponsors. The bibs brings in about $50 million a year, according to the complaint filed in the Northern District of California on Tuesday, but the caddies never see a penny.