Moores v. Citizens' National Bank of Piqua was a case heard by the United States Supreme Court in 1884. The case involved a dispute between the Citizens' National Bank of Piqua and the Moores, a family of creditors. The Moores had loaned money to the bank and had taken a mortgage on the bank's property as security for the loan. When the bank failed to pay the loan, the Moores sought to foreclose on the mortgage. The bank argued that the foreclosure was invalid because the mortgage was not properly recorded. The Supreme Court held that the Moores were entitled to foreclose on the mortgage. The Court reasoned that the Moores had taken reasonable steps to protect their interests by obtaining a mortgage on the bank's property. The Court also held that the bank had failed to comply with the state's recording laws, and thus the Moores were not required to record the mortgage in order to be able to foreclose on it. The Court concluded that the Moores were entitled to foreclose on the mortgage and recover the money they had loaned to the bank.

Justice Harlan delivered the dissenting opinion in Moores v. Citizens' National Bank of Piqua, arguing that the Court's decision was contrary to established precedent and would lead to a dangerous expansion of federal power over state law. He argued that Congress had not intended for national banks to be able to sue in federal court on matters concerning state laws, as this would allow them an unfair advantage over other businesses operating within the same jurisdiction. Furthermore, he noted that allowing such suits could potentially interfere with states’ ability to regulate their own banking systems without interference from the federal government. In conclusion, Justice Harlan urged caution when expanding congressional authority beyond what is explicitly stated by statute or otherwise provided for under existing case law.