BILLINGS, Mont. -

A Washington state man faces sentencing Friday in federal court on charges he led an interstate meth-trafficking ring that exploited workers in eastern Montana's oil patch.

Robert Farrell Armstrong of Moses Lake, Washington, will appear before U.S. District Judge Susan Watters in Billings.

Under a deal with prosecutors, he pleaded guilty in January to possession with intent to distribute methamphetamine.

Prosecutors want Armstrong sent to prison for roughly two decades.

They say the 50-year-old defendant ran a network of dealers and enforcers selling large quantities of almost-pure meth in eastern Montana.

Armstrong's public defender, Anthony Gallagher, is seeking a 10-year sentence. Gallagher says prosecutors overstated Armstrong's leadership role in the trafficking ring.

Eleven others arrested with Armstrong last year were previously sentenced.