Native American tribes got a big win in August when a federal court upheld the Indian Child Welfare Act, a pivotal 1978 law that requires states to prioritize placing Native children in foster or adoptive homes with Native families over non-Native families.

But the decision by a three-judge panel of the U.S. Court of Appeals for the 5th Circuit is now being reconsidered by the full court, which announced earlier this month that it is granting a rehearing in a case known as Brackeen v. Bernhardt.

Its the most consequential challenge to ICWA since its inception, and tribes fear a ruling against the law could threaten all tribes inherent sovereignty. Thats because the plaintiffs in the case, a non-Native couple trying to adopt a Native child, are arguing that ICWA is race-based and violates the equal protection clause in the Constitution.

If #ICWA opponents in Brackeen v. Bernhardt are successful, it will potentially impact the sovereignty of every tribe, because the plaintiffs view tribes as racial entities, not sovereign governments, the Cherokee Nation tweeted in March .

The reason ICWA exists at all is because Congress wanted to try to remedy to an ugly period in American history: For decades, the U.S. government took tens of thousands of Native children away from their families on reservations, sometimes forcibly, and put them in boarding schools or placed them with white families to assimilate them into white culture.