Shelley v. Kraemer

Some people made a contract not to allow Blacks to live in a certain neighborhood. When a Black person bought some land in the neighborhood, they sought judicial remedy.

Whether enforcement by state courts of the restrictive agreements in these cases may be deemed to be the acts of those States; and, if so, whether that action has denied these petitioners the equal protection of the laws which the Amendment was intended to insure.

Can a racially discriminatory housing covenant be enforced in US courts since it is private discrimination?

Yes, equal protection has been denied by the State's actions.

The actions of state courts and judicial officers in their official capacities are to be regarded as action of the State within the meaning of the 14th amendment.