Read this and answer the question

Though Decca would continue to keep picture budgets lean, it was favored by changing circumstances in the film business, as other studios let their contract actors go in the wake of the 1948 U.S. vs. Paramount Pictures, et al. decision. Leading actors were increasingly free to work where and when they chose, and in 1950 MCA agent Lew Wasserman made a deal with Universal for his client James Stewart that would change the rules of the business. Wasserman's deal gave Stewart a share in the profits of three pictures in lieu of a large salary. When one of those films, Winchester '73, proved to be a hit, the arrangement would become the rule for many future productions at Universal, and eventually at other studios as well.

What legal decision resulted in movie studios letting their contract actors go?
U.S. vs. Paramount Pictures, et al.