TULSA, Okla. (AP) — A couple's lawsuit contends that an Oklahoma law allowing tribes to intervene in private adoption cases involving Native American children violates their constitutional rights.

The Tulsa World reports that the Oklahoma Indian Child Welfare Act permits tribes to interfere even when both birth parents oppose such action and have agreed on who they want as adoptive parents for their child.

The lawsuit says the couple, who are both 18, was upset the Cherokee Nation could intervene with their adoption plan since the birth mother is enrolled in the tribe. The prospective, adoptive parents have joined the couple in the lawsuit, which was filed last week in Tulsa federal court.

An assistant attorney general for the Cherokee Nation says the tribe plans to vigorously defend the law.