The Ex parte IN THE MATTER OF HARLEY-DAVIDSON MOTOR COMPANY et al., 1921, is a U.S. Supreme Court case that revolved around the issue of patent infringement. Harley-Davidson Motor Company and others had filed a petition against Excelsior Motor Manufacturing & Supply Co., alleging that they were infringing on their patented motorcycle design. The court was asked to decide whether or not an injunction should be issued to prevent Excelsior from continuing to manufacture motorcycles using the disputed design while the lawsuit was ongoing. Ultimately, it was ruled in favor of Harley-Davidson with an issuance of a temporary injunction against Excelsior until the final determination could be made regarding patent validity and infringement.

The dissenting opinion in the case of Ex parte IN THE MATTER OF HARLEY-DAVIDSON MOTOR COMPANY et al., 1921, argued that the majority's decision to deny Harley-Davidson's petition for a writ of mandamus was incorrect. The dissent believed that the lower court had exceeded its jurisdiction by ordering an interlocutory injunction against Harley-Davidson without sufficient evidence or cause. They contended that this action violated due process and infringed upon Harley-Davidson’s rights as it effectively forced them into compliance with an order they were contesting legally. Furthermore, they disagreed with the majority's interpretation of "discretion," arguing instead for a more narrow understanding which would limit judicial power and protect individual rights from potential abuses.