The U.S. Supreme Court case Trump v. Mazars USA, LLP in 2019 revolved around the issue of whether or not President Donald Trump's financial records could be subpoenaed by Congress for investigative purposes. The House Committee on Oversight and Reform had issued a subpoena to Mazars USA, an accounting firm used by Trump, seeking years of his financial documents as part of their oversight responsibilities. In response, President Trump sued to block the release of these documents arguing that it was politically motivated and exceeded Congressional authority. The Supreme Court ruled in favor of neither party directly but sent the case back down to lower courts with instructions for them to further scrutinize whether there is a significant legislative purpose behind the subpoenas which would justify such an invasive step into personal finances.

In the dissenting opinion for Trump v. Mazars USA, LLP, Justice Thomas argued that Congress has no power to issue a legislative subpoena for private, non-official documents—whether they belong to the President or not—unless it is seeking information to legislate within its constitutional authority. He contended that this case did not meet those criteria and thus disagreed with the majority's decision. According to him, there was no legitimate legislative purpose behind these subpoenas; rather he saw them as an attempt by Congress to delve into private affairs of the President for political purposes. Furthermore, he expressed concern over potential abuses of power if such broad interpretation of congressional subpoena powers were allowed without any clear boundaries set forth in law or precedent.