O'Brien v. Smith was a case heard before the United States Supreme Court in 1861. The dispute arose when O'Brien, an Irish immigrant living in Massachusetts, attempted to purchase land from Smith but was refused due to his foreign status. O’Brien sued for damages and argued that he had been denied equal protection under the law as guaranteed by the Fourteenth Amendment of the Constitution. The court ruled against him on grounds that there were no laws preventing aliens from purchasing property at that time; thus, they could not be held liable for discrimination based on nationality or race alone. However, this decision did set a precedent which would later be used to protect immigrants and other minority groups from being discriminated against in similar situations.

In O'Brien v. Smith, the Supreme Court was asked to decide whether a state law that allowed for an individual to be held liable for debts incurred by their spouse violated the Constitution's Contract Clause. The majority opinion found that it did not violate the clause and upheld the law in question. However, Justice Grier dissented from this decision, arguing that such a law would create an undue burden on individuals who had no control over their spouses’ actions and could potentially lead to them being unfairly punished or having their property taken away without due process of law. He argued further that if states were allowed to pass laws like these then they would have too much power over citizens’ private affairs which is something prohibited by both common sense and constitutional principles. Ultimately he concluded that while states should have some authority when it comes to regulating contracts between married couples, they must do so within reasonable limits set forth by federal laws as well as those outlined in the Constitution itself.