type: timeline_event Business leaders including Henry Clay Frick, Judge Elbert Gary, and John D. Rockefeller Jr. launched a coordinated campaign to roll back labor gains by promoting the "open shop" as patriotic while branding union membership as "un-American." Meeting in Chicago in 1921, anti-union employers agreed not to negotiate with unions and to require employees to sign pledges against union membership. The National Association of Manufacturers endorsed the strategy in 1920, combining yellow-dog contracts, welfare capitalism, company unions, and outright repression to control workplaces and prevent unionization. The campaign drove union membership down at least 25 percent between 1921-1923, with total membership falling from 5.1 million in 1920 to 3.6 million in 1929. U.S. Steel required workers to sign a "Pledge of Patriotism" promising not to strike. The IBEW condemned the American Plan as an attempt to "camouflage industrial slavery with the American flag," but the coordinated corporate assault successfully suppressed labor organizing throughout the decade.