The Irishman claimed the vacant belt this month with a dramatic stoppage win over the previously unbeaten Matt Korobov in Las Vegas. ??
Saunders was waiting for the winner after his recent points win over Chris Eubank Jr earned him the status of mandatory challenger, and the governing body have called for Lee to face him early in the New Year.
A statement on the WBO website read: ???Please be advised that the parties have 30 days (starting on December 13, the date in which Mr Lee won the WBO middleweight championship of the world) to negotiate an agreement for the WBO championship bout between Andy Lee and Billy Joe Saunders.
???If an accord is not reached between January 12, 2015, a purse bid will be ordered.???
The 25-year-old Saunders, a southpaw like Lee, extended his unbeaten record to 21 wins with his split decision triumph over Eubank Jr in November.
But he will take a step up in class against the experienced champion, who is enjoying a resurgence under the tutelage of trainer Adam Booth.