In Fong Haw Tan v. Phelan, the U.S Supreme Court ruled in favor of Fong Haw Tan, a Chinese immigrant who had been convicted of manslaughter and was facing deportation under immigration laws that allowed for the removal of aliens who committed crimes involving "moral turpitude." The court held that while his crime was serious, it did not necessarily involve moral turpitude as defined by immigration law. The ruling emphasized that ambiguities in laws relating to deportation should be interpreted in favor of the alien due to its severe consequences. This case set an important precedent regarding how criminal convictions affect an individual's immigration status and established a principle known as the "rule of lenity," which states that any ambiguity or doubt about whether a law applies to someone should be resolved in their favor.

In the dissenting opinion for Fong Haw Tan v. Phelan, Justice Robert H. Jackson disagreed with the majority's interpretation of immigration law concerning deportation based on criminal convictions. He argued that Congress intended to make a distinction between crimes involving moral turpitude and those not involving such conduct when determining eligibility for deportation. According to him, this was evident in the language used by Congress which referred specifically to "crime" rather than "offense". Therefore, he believed that Fong Haw Tan's conviction for involuntary manslaughter should be considered a crime involving moral turpitude and thus grounds for his deportation under existing laws at that time.