In the case of Caban v. Mohammed et ux., 1978, the U.S. Supreme Court ruled that a New York law was unconstitutional because it treated unwed mothers and fathers differently in adoption proceedings. The law allowed unwed mothers to block an adoption without showing they were fit parents, but did not give this right to unwed fathers unless they had legitimized their relationship with the child by living with them and supporting them financially. Pedro Caban, an unmarried father who had maintained contact with his children after separating from their mother, challenged this when she and her husband sought to adopt the children without his consent. The court held that there was no substantial difference between unmarried mothers and fathers regarding their ability to develop deep emotional ties with their children or act as effective parents; thus treating them differently violated equal protection principles under Fourteenth Amendment of Constitution.

In the dissenting opinion for Caban v. Mohammed, Justice Stewart, joined by Chief Justice Burger and Justices Rehnquist and Stevens, argued that the majority's decision was a misinterpretation of the Equal Protection Clause. They contended that there is a rational basis for New York law to distinguish between unmarried mothers and fathers in adoption cases because of biological differences between men and women. The dissenters believed it reasonable to assume that an unwed mother has established care for her child while an unwed father may not have done so. Therefore, they argued it was justified to require consent from only the mother in these circumstances as she would be more likely to act in the best interest of her child due to this bond formed through caregiving responsibilities. This interpretation respects both state sovereignty over family law matters and acknowledges inherent gender differences without violating equal protection rights.