In 2007 the Cherokee passed an amendment to its constitution that required members to have Cherokee blood.
The US government has stepped into a bitter ethnic dispute between a powerful Native American tribe and the descendants of black slaves the tribe used to own.
The argument touches on some of the most difficult and heartbreaking chapters in American history, encompassing the brutal treatment of Native Americans as well as the bitter legacy of slavery.
The fight centres on the tribal membership of the Cherokee nation, a Native American group who were kicked out of their ancestral lands in south-eastern America and forced to relocate to Oklahoma.
For a long time, the tribe has included among its members people who called themselves 'freedmen', who were descendants of the black slaves that the tribe used to own, but who were given their liberty after the American civil war. Being a member of the tribe gives certain rights and benefits around tribal-run healthcare schemes, and the spending of money the tribe earns from casino operations.
However, the Cherokee's tribal leadership has recently moved to expel an estimated 2,800 freedmen from the tribal rolls, which will cut off their access to Cherokee services and also stop them from voting in upcoming tribal elections. In 2007 the tribe passed an amendment to its constitution that required members to have Cherokee blood. The dispute has been fiercely fought on all sides amid accusations of greed and racism.
But now the US Bureau of Indian Affairs has weighed in.
Larry Echo Hawk, the assistant secretary at the department, has written a letter to the Cherokee saying it will not recognise any election the tribe carries out that does not include the freedmen.
Echo Hawk wrote that the government considered that a treaty signed in 1866 made provision for including the freedmen on Cherokee tribal rolls, and that that right could not be taken away.
"The department's position is, and has been, that the 1866 treaty between the United States and the Cherokee nation vested Cherokee freedmen with rights of citizenship in the nation, including the right of suffrage," Echo Hawk wrote.
He warned that any election held without the freedmen would not be seen as lawful by the US government.
"The department will not recognize any action taken by the nation that is inconsistent with these principles and does not accord its freedmen members full rights of citizenship," he wrote.
In a statement, the acting principal chief of the Cherokee nation, Joe Crittenden, vowed that the tribe would press on with the coming election.
"We will hold our election and continue our long legacy of responsible self-governance," Chittenden said.
That move now puts the tribe on a collision course with the government, but Chittenden was defiant that the tribe would not be dictated to by a Washington government department.
"The Cherokee nation will not be governed by the BIA," he said.