Osage Nation voters will consider next week whether to issue marriage licenses to same-sex couples.
The tribe already recognizes gay marriages from other jurisdictions, but its legal code still defines marriage as a "personal relation between a man and a woman." Monday's vote is on whether marriage should be defined as a "personal relation between two persons."
The tribe has about 15,000 eligible voters. As of last Monday, the tribe had received 1,070 absentee ballots.
The Tulsa World reported Friday that only a handful of tribes nationwide conduct or recognize same-sex marriages.
In December, the Cherokee Nation's attorney general said a 2004 law limiting marriage to heterosexual couples was unconstitutional. The Cherokee Nation Tribal Council has a committee hearing scheduled for Tuesday to consider referring the issue to voters.