GREAT FALLS, Mont. (AP) – A debate over whether to expand the eligibility requirements to enroll as a Blackfeet tribal member is dividing the northwestern Montana reservation.

Enrolled members qualify for more health and social service benefits, plus they get to vote on tribal matters and hold office within the nation. But on both sides, the bigger question is whether expanding enrollment will create greater unity or threaten the tribe's existence.

For the past 50 years, Blackfeet tribal eligibility has been determined by whether a person is at least one-quarter Blackfeet, meaning that at least one grandparent must be a full-blooded Blackfeet. A majority of federally recognized tribes use that measure, known as blood quantum, to determine eligibility, according to the Oklahoma Indian Affairs Commission.

But an organization called Blackfeet Enrollment Amendment Reform is collecting signatures for a petition seeking to change that standard. Its members want enrollment eligibility to include anyone who has proof of being the child, grandchild or great-grandchild of an enrolled tribal member.

Supporters say the change would lead to more tribal inclusion and unity.

Those opposed to the proposed lineal descent eligibility include members of the Blackfeet Against Open Enrollment movement, who say blood quantum separates those with a close affiliation to Native American life and cultural values from others with little or no personal connection to their ancestral heritage.

The Blackfeet tribe in 2011 had 16,924 enrolled members, according to tribal enrollment office statistics. But there are about 105,000 people who identified themselves as `Blackfeet Indian' on the 2010 U.S. Census.

The Blackfeet's original constitution, written in 1935, included a requirement that tribal members be at least 1/16th Blackfeet. The constitution was amended in 1962 to raise that requirement to a quarter.

All Blackfeet children living on the reservation prior to Aug, 30, 1962, were also included as tribal members. But in some cases their children do not meet the blood quantum requirement and are excluded from tribal rolls.

Robert Hall's parents are enrolled members but with a 15/64 blood quantum, he is not. He grew up on the reservation, speaks the Blackfeet language and identifies with Blackfeet cultural values.

Hall told the Great Falls Tribune that he believes blood quantum system is racist.

“We are literally living in a caste system – people with certain genetic qualities who are denied access to resources because of their racial makeup. If any other group in America was advocating this type of racial purity, they would be condemned as racists,” Hall said.

Opponents of the proposed change are angered by racism allegations, saying those advocates are in effect campaigning to assimilate the Blackfeet people into white culture. Within a few generations, the cultural and ethnic characteristics that make the Blackfeet people unique would be lost by expanding enrollment, they said.

“When we go back and we look through history, Indians have fought assimilation and we have won – and we're still winning today,” said Nathan DeRoche, an enrolled tribal member and an opponent of expanded enrollment. “But if we open that enrollment, they have won. Then we are a defeated people.”