In the 1920 case of Missouri Pacific Railroad Company et al. v. Ault, the U.S Supreme Court ruled in favor of Missouri Pacific Railroad Company and against Ault, who had sued for damages after a train accident caused by alleged negligence on part of the railroad company's employees. The court held that under federal law, an employer is not liable for injuries to an employee if they are due to risks inherent in their employment or those created by fellow servants' negligence unless it can be proven that there was some fault on part of the employer such as failure to provide safe tools or sufficient manpower etc., which wasn't established in this case. This ruling reinforced what is known as "fellow servant rule", limiting employers’ liability when workers were injured due to actions taken by co-workers during regular job duties.

In the dissenting opinion for Missouri Pacific Railroad Company et al. v. Ault, it was argued that the court majority had erred in its interpretation of state law and overstepped its jurisdiction by interfering with a matter of local concern. The dissenting justices believed that the case should have been decided based on Missouri's laws rather than federal ones, as it involved a dispute between private parties within one state only - not interstate commerce or any other federal issue. They also disagreed with the majority's view that railroad companies could be held liable for damages caused by sparks from their locomotives under all circumstances; instead, they felt this liability should depend on whether reasonable precautions were taken to prevent such accidents. In essence, they contended that railroads shouldn't be treated as insurers against all possible harm but only held accountable when negligence can be proven.