In the case of Wong Yang Sung v. McGrath, Attorney General et al., 1949, the U.S. Supreme Court ruled that deportation hearings must be conducted in accordance with the Administrative Procedure Act (APA). The petitioner, Wong Yang Sung, was a Chinese immigrant who had been ordered to be deported by an immigration inspector acting as both prosecutor and judge during his hearing. This dual role was found to violate APA's requirement for separation of functions among officers engaged in adjudication or rulemaking proceedings. The court held that such violation rendered the proceeding unfair and voided its result - ordering Mr. Sung’s deportation from America back to China.

The dissenting opinion in the case of Wong Yang Sung v. McGrath, Attorney General, et al., argued that the majority's decision to apply provisions of the Administrative Procedure Act (APA) retroactively was incorrect. The dissenters believed that this interpretation contradicted Congress' intent when passing the APA and would lead to unnecessary complications and delays in deportation proceedings. They also disagreed with the majority's view on what constituted a "hearing" under immigration law, arguing that it did not necessarily require formal procedures like those found in court trials. Furthermore, they contended that even if there were procedural flaws in Wong Yang Sung's hearing before an Immigration Service investigator who had prosecutorial functions as well, these could have been corrected by subsequent review processes within administrative agencies or courts without necessitating a new trial-like hearing.