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; 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.
Quote from 16B Am. Jur. 2d § 861:
""Intermediate scrutiny," wherein a challenged classification need only further a substantial state interest, is employed only in limited circumstances when legislation is not facially or constitutionally invidious but nonetheless gives rise to some recurring constitutional difficulties. In the case of sex or gender discrimination or illegitimacy, for instance, the proper standard to apply is the intermediate scrutiny standard.
To withstand intermediate scrutiny under an equal protection analysis, a statutory classification must be substantially related to an important governmental objective. In determining whether governmental objectives for making a classification are important as a step in an equal protection challenge of a statute under intermediate scrutiny, the burden of justification is demanding and it rests entirely on the state. To survive "intermediate scrutiny" in an equal protection challenge, a statute must not only further an important governmental interest and be substantially related to that interest but the justification for the classification must also be genuine and must not depend on broad generalizations. Where proffered governmental interests are sufficiently weighty to be called important, as a step in an equal protection challenge of a statute under intermediate scrutiny, the critical inquiry is whether these governmental objectives can fairly be said to be advanced by the legislative classification. Under intermediate scrutiny in an equal protection challenge to a statute, the relationship between the government's goal and the classification employed to further that goal must be substantial; in order to evaluate that relationship, it is helpful to consider whether the legislation is overinclusive or underinclusive."