In Simler v. Conner (1962), the U.S. Supreme Court ruled that federal courts have jurisdiction over cases involving legal disputes between parties from different states, even if the dispute involves state law issues. The case involved a fee dispute between an attorney and his client who were residents of different states. The attorney filed suit in federal court under diversity jurisdiction, which allows citizens of different states to litigate disputes in federal court when the amount in controversy exceeds $75,000. Although the lower courts held that this was essentially a malpractice claim requiring application of state law and thus not appropriate for diversity jurisdiction, the Supreme Court disagreed and found it was primarily a contract action concerning fees owed by one party to another - something within purview of diversity jurisdiction.

In the dissenting opinion for Simler v. Conner, Justice Clark argued that the case should be decided based on state law rather than federal law. He pointed out that both parties were from the same state and their dispute was over a fee contract, which is typically governed by local laws. Furthermore, he noted that there was no diversity of citizenship in this case to warrant its removal to federal court under 28 U.S.C §1332(a). The majority's decision to apply federal common law instead of state law seemed arbitrary and inconsistent with previous rulings where similar cases were remanded back to state courts due to lack of jurisdiction. In his view, it would have been more appropriate for the Supreme Court not only respect but also defer matters such as these - involving purely private disputes without any substantial federal interest -to individual states' legal systems.