On Wednesday night, the council voted unanimously to launch an investigation into whether backers committed election fraud when they gathered signatures.
The initiative for an upcoming ballot would move the proposed $2 billion South Mountain Freeway onto tribal soil.
If approved, the ballot language would ask voters by June 20 if they support or oppose allowing the 22-mile Loop 202 extension on the reservation.
The tribe’s police and auditors were directed to report their findings in 30 to 60 days.
The Arizona Republic says the council is required to decide by April 21 whether to put the measure on a ballot, refuse it or legislate a course of action based on the signatures.