Erdman Act

The Erdman Act of 1898 was a United States federal law pertaining to railroad labor disputes. The law provided for arbitration for disputes between the interstate railroads and their workers organized into unions.
Major provisions.
The most significant portion of the act was its provision prohibiting a railroad company from demanding that a worker not join a union as a condition for employment (Section 10). 
The interstate requirement meant that the law affected individuals who worked on the moving trains, such as firemen, brakemen, telegraphers, and conductors, providing that the train transported freight and passengers between states. Workers who maintained railroad cars and station clerks did not come under the statute's jurisdiction. While the arbitration system created by the act was voluntary, the results were binding if all sides agreed to arbitration.
Capital and labor each chose one of three arbitrators under the act; if they could not agree upon a third, the government would. The Chair of the Interstate Commerce Commission and the United States Commissioner of Labor, acting in concert, made that choice under those circumstances.
The act made it unlawful to strike or fire a worker during the arbitration process; it also made it illegal to terminate the employment of a worker involved in the dispute while arbitration was pending, except for neglecting duty or inefficiency. 
In "Adair v. United States" (1908), the United States Supreme Court declared Section 10 of the Erdman Act unconstitutional.