The rationale for this legal action lay in the fact that the Mail was transported by rail—transport which was interrupted when trains including Pullman cars were stopped in their tracks. Under the Sherman Anti-Trust Act of 1890, which ruled it illegal for any business combination to restrain trade or commerce, an injunction was issued on July 2 enjoining the ARU leadership from "compelling or inducing by threats, intimidation, persuasion, force or violence, railway employees to refuse or fail to perform their duties". The next day, President Cleveland ordered 20,000 federal troops to crush the strike and run the railways.