The Supreme Court of the United States (SCOTUS) upheld a law that gives Native American families priority in adoptions and foster care placements of tribal children.

In a 7-2 vote on Thursday, the nation's highest court rejected challenges to the Indian Child Welfare Act (ICWA) brought by a non-Native American couple seeking to adopt an Indian child and the state of Texas.

They had argued that the ICWA, passed by Congress in 1978, was unconstitutional and discriminates on the basis of race.

"The issues are complicated," said Justice Amy Coney Barrett, who authored the majority opinion.

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"But the bottom line is that we reject all of petitioners' challenges to the statute, some on the merits and others for lack of standing," said Barrett, who is herself the mother of two adopted children of Haitian origin.

Like in Canada, Native American children in the United States were for decades removed from their biological parents and placed in boarding schools or with non-Indigenous families as part of a policy of forced assimilation.

Congress sought to bring an end to the practice with the passage of the ICWA, which set strict standards for removing Native American children from their parents and required tribal families to receive priority for foster care placements and adoptions.

Republican-led Texas, as well as families restricted by the ICWA from adopting Native American children, filed a legal challenge under the US Constitution's 14th Amendment, which limits the differentiation between citizens on the basis of race.

Several Native American tribes, backed by the administration of President Joe Biden and the powerful ACLU rights organization, countered that the law was not based on race but on Indigenous groups' sovereign rights.

Under US law, Native American tribes have a special status with their own legal jurisdictions and court systems.

President Biden welcomed the court ruling.

"Our Nation's painful history looms large over today's decision," the president said in a statement. "In the not-so-distant past, Native children were stolen from the arms of the people who loved them.

"The Indian Child Welfare Act was passed to protect the future of Tribal Nations and promote the best interests of Native children, and it does just that."

The ACLU called the ruling a "landmark victory for tribal sovereignty."

"Tribes have a fundamental right to govern themselves and make decisions on issues that affect their own people – including Native children – without interference from federal or state governments," said Crystal Pardue, staff attorney in the ACLU's Racial Justice Program.