This anti-union pledge was also called an "iron clad document," and from this time until the close of the 19th century "iron-clad" was the customary name for the non-union promise.
Beginning with New York in 1887, sixteen states wrote on their statute books declarations making it a criminal act to force employees to agree not to join unions.
The Congress of the United States incorporated in the Erdman Act of 1898 a provision relating to carriers engaged in interstate commerce.
The strike proved a failure, and a large number of employers required oral or written promises to abandon and remain out of the organization as a condition of re-employment.
The section of the Erdman Act making it criminal to force employees to sign anti-union agreements therefore remained unadjudicated.