Yick Wo v. Hopkins, Sheriff is a landmark United States Supreme Court case that established the principle of equal protection under the law. The case involved Yick Wo, a Chinese immigrant who was denied a permit to operate a laundry in San Francisco, California, despite meeting all the requirements for the permit. The city of San Francisco had passed a law that required all laundry businesses to obtain a permit, but the law was enforced in a discriminatory manner, with all Chinese applicants being denied permits while non-Chinese applicants were granted them. Yick Wo challenged the law in court, arguing that it violated the Fourteenth Amendment's Equal Protection Clause. The Supreme Court agreed, ruling that the law was unconstitutional because it was enforced in a discriminatory manner. The Court held that the law was not only discriminatory on its face, but that it was also applied in a discriminatory manner. This ruling established the principle that laws must be applied equally to all persons, regardless of race or ethnicity. The Court's decision in Yick Wo v. Hopkins, Sheriff has been cited in numerous subsequent cases involving equal protection under the law.

Justice Field delivered the dissenting opinion in Yick Wo v. Hopkins, Sheriff. He argued that the San Francisco ordinance was discriminatory and violated both the Fourteenth Amendment of the United States Constitution as well as Section 1977 of the Revised Statutes which prohibited any state from denying to any person within its jurisdiction "the equal protection of laws." Justice Field noted that while it may be true that all persons were technically subject to this law, it was only enforced against Chinese laundry owners who had been denied permits due to their race or nationality. Furthermore, he pointed out how other non-Chinese applicants with similar violations were granted permits without issue while those owned by Chinese people were not given a chance at obtaining one. This showed clear evidence of discrimination on behalf of San Francisco's Board of Supervisors and thus violated constitutional rights protected under federal law. In conclusion, Justice Field believed that Yick Wo should have his permit reinstated since he had been wrongfully denied based solely on his race or national origin rather than for legitimate reasons related to public health and safety concerns outlined in city ordinances.