In the case of Mathews, Secretary of Health, Education and Welfare v. Lucas et al., 1975, the Supreme Court ruled on a challenge to provisions in the Social Security Act that determined eligibility for survivor's benefits based on legitimacy at birth. The plaintiffs argued these provisions discriminated against illegitimate children by making it more difficult for them to qualify for benefits after their father’s death compared to legitimate children. The court held that while there was differential treatment between legitimate and non-legitimate children under this law, such differentiation did not violate equal protection principles because they were reasonably related to a legitimate government interest - namely preventing fraudulent claims and promoting administrative efficiency within social security system. Therefore, the court upheld these contested sections of Social Security Act as constitutional.

In the dissenting opinion for Mathews v. Lucas, Justice Brennan disagreed with the majority's ruling that certain provisions of the Social Security Act were constitutional. He argued that these provisions discriminated against illegitimate children by denying them survivor benefits unless they could prove their deceased parent had been either living with or supporting them at the time of death - a requirement not imposed on legitimate children. Brennan contended this was an unjustifiable discrimination violating equal protection principles under Fifth Amendment due process clause. He believed there was no rational basis to assume illegitimate children are less likely to be dependent on their parents than legitimate ones and such assumption perpetuates stereotypes about non-marital families being less deserving of legal protections than marital ones, which is constitutionally unacceptable.