14th Amendment, Section 1: All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States [emphasis added]; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.
Regarding business owners using 14A to protect themselves from misguided, pro-LGBT state officials and other likewise low-information LGBT supporters, note that Acts 22:23-30 indicates that Paul claimed his rights as a Roman citizen to save himself from being flogged.
Which probably won’t work at most modern trial court levels. It takes a trip to the appellate level at least, and the modern issues that have been raised have scarcely even gotten there.