A unanimous Supreme Court on Monday stuck down a law that makes birthright citizenship harder for children of unwed fathers to obtain than children of unwed mothers.

The court held in an 8-0 ruling the gender line Congress drew in the Immigration and Nationality Act of 1952 is “incompatible” with the Fifth Amendment’s requirement that all people must be treated equally under the law.

The law requires unwed fathers to have 10 total years of U.S. residency, including five years after the age of 14, to confer citizenship on a child of theirs who is born overseas. Unwed American mothers, meanwhile, are only subject to a 1-year U.S. residency requirement to give their children U.S. citizenship.

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In delivering the opinion of the court, Justice Ruth Bader Ginsburg said the equal protection infirmity in requiring a longer requirement for unwed fathers than for unwed mothers is clear. Nonetheless, the court couldn’t grant Luis Ramon Morales-Santana — the plaintiff in the case — relief.

A felon, Morales-Santana challenged the law after the Board of Immigration Appeals denied his claim that he was a U.S. citizen and couldn’t be deported because his mother was Dominican and his father was American.

The board said Morales‐Santana’s father had not satisfied the physical residency requirements for unwed fathers since he left the U.S. when he was 18 years old, 20 days shy of his 19th birthday and fifth year of residence in the U.S.

Ginsburg said it’s up to Congress to decide whether to extend the shorter residency requirement to unwed fathers.

In the interim, she said the law’s five-year requirement should apply, prospectively, to children born to unwed U.S.-citizen mothers.

New Justice Neil Gorsuch took no part in considering or deciding this case.