WASHINGTON — The Supreme Court on Thursday upheld the landmark federal adoption law that seeks to keep Native American children with tribal families.

By a 7-2 vote, the justices rejected a constitutional challenge from a white Texas couple and Texas state attorneys who contended the adoption preferences for Native Americans amounted to unconstitutional discrimination based on race.

“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 Justice Amy Coney Barrett for the court.

Justices Thomas Clarence and Samuel A. Alito Jr. dissented.

The law was defended by Interior Secretary Deb Haaland, the first Native American to serve as a Cabinet secretary.

Congress passed the Indian Child Welfare Act in 1978 after it found “an alarmingly high percentage of Indian families are broken up by the removal, often unwarranted, of their children from them.” These children were being raised instead in boarding schools or by non-Native families.

The law gave a role to tribal leaders in arranging adoptions and called for placing Native children with members of their extended family or their tribe or members of another tribe.

But these preferences were challenged as unconstitutional by Chad and Jennifer Brackeen, a Texas couple who had taken in two children shortly after their birth with the approval of their mother, who was a Navajo. Tribal authorities later tried to remove the children from the white family and send them instead to a Navajo couple who lived several hundred miles away.

The Brackeens sued and argued that decisions about adoptions should be based on the “best interest of the child,” not the interest of the tribe.