The Indian Child Welfare Act is facing its biggest legal challenge since the law was enacted more than four decades ago. More than 20 states have joined hundreds of tribes, advocacy groups and the federal agency overseeing Indian affairs to urge an appellate judge to uphold the law Wednesday.

A Texas couple fostered a baby eligible for membership in both the Navajo and Cherokee tribes. The state denied their request to adopt him after the Navajo Nation found a potential home with a Navajo family. Then the placement fell through and the couple was able to adopt the boy. And now they want to adopt his younger half-sister.

A federal judge in Texas ruled the Indian Child Welfare Act is unconstitutional, saying it is racially motivated and violates the equal protection clause. Opponents say tribes are a political classification, not a racial one, and overturning the law would lead to damage in tribal communities.

Congress passed the Indian Child Welfare Act in 1978 because a high number of Native American children were being removed from their homes without a significant reason. The law requires states to seek placement with the child's extended family, members of the child's tribe or other Native American families.