The Mayor v. Lord was a United States Supreme Court case that was decided in 1869. The case involved a dispute between the mayor of the City of New York and a man named Lord. Lord had been arrested for disorderly conduct and was taken to the mayor's office to be tried. The mayor found Lord guilty and sentenced him to pay a fine. Lord refused to pay the fine and was taken to jail. Lord then filed a writ of habeas corpus, claiming that the mayor had no authority to try him and that he should be released from jail. The Supreme Court agreed with Lord and ruled that the mayor had no authority to try him. The Court held that the mayor was not a court of record and did not have the power to try criminal cases. The Court also held that the mayor had no authority to impose a fine or sentence someone to jail. The Court's decision in The Mayor v. Lord established that mayors do not have the authority to try criminal cases and that they cannot impose fines or sentences. This decision has been cited in numerous cases since then and has been used to support the idea that mayors do not have the power to try criminal cases.

In the case of The Mayor v. Lord, the Supreme Court was tasked with determining whether a city ordinance that prohibited certain types of businesses from operating within its limits violated the Fourteenth Amendment's Equal Protection Clause. In an 8-1 decision, it was held that such ordinances were constitutional and did not violate any rights under the clause. Justice Field wrote a dissenting opinion in which he argued that while cities may have some authority to regulate their own affairs, they cannot do so at the expense of fundamental rights guaranteed by federal law. He further argued that this particular ordinance had no legitimate purpose other than to discriminate against certain classes of people and thus should be struck down as unconstitutional.