Tyson Fury is entitled to a greater share of the purse for his rematch against heavyweight champion Deontay Wilder, says the WBC.
Britain's Fury and American Wilder shared a controversial and thrilling draw in Los Angeles in December.
The WBC has told their promoters to agree a rematch by 5 February.
If there is no agreement, the WBC will split the purse bid 60-40 in favour of Wilder, "considering the market value of Fury".
This is an increase from the 30% that is typically due to the challenger in a title fight.
The WBC sanctioned a direct rematch between Fury and Wilder last month, ensuring the American did not have to face mandatory challenger Dominic Breazeale next.
Fury's promoter Frank Warren and Wilder's promoter Shelly Finkel will now negotiate but if they do not agree an acceptable fee for both fighters by the deadline, the fight is open to sealed bids from other promoters, with the highest bid winning.
If that happens, Fury would then be entitled to 40% of the purse.
Earlier this month, Warren told BBC Sport that Fury was a bigger draw than heavyweight champion Anthony Joshua.
Joshua has a date booked at Wembley Stadium on 13 April for his next fight and a unification bout with Wilder is the number one target.
But Wilder has been more open to fighting Fury and Warren believes Joshua - promoted by Eddie Hearn - is wary of a contest with his man.
Although Fury was knocked down in the ninth and 12th rounds against Wilder, many observers thought the 30-year-old Briton should have won the bout, which was scored 115-111 for Wilder, 114-112 for Fury and 113-113.
Fury said he had "never seen a worse decision in my life" and described it as a "gift" for his opponent.
Wilder, 33, questioned if referee Jack Reiss' count was too slow in Fury's remarkable rise from the canvas in the 12th round, which Reiss denied.