Lee Doyle, who manages snooker stars including Ronnie O'Sullivan and Stephen Hendry, has quit the board of the sport's governing body.
The 100sport Group chairman objects to proposals to give Barry Hearn a 51% stake in World Snooker as part of his plans to revitalise the game.
Hearn said that as a rival promoter - "effectively a competitor" - Doyle's position had become "untenable".
Doyle said he had "agreed to disagree" with Hearn over his controlling stake.
Having become World Snooker's chairman last December, Hearn will take a controlling interest if his ideas are backed by a majority of the players at a meeting on 5 May.
Several, including O'Sullivan and world champion John Higgins, have already given him their support, with Hearn promising to stand down from his position if players do not back his plans.
Doyle's departure comes just five days before the start of the World Championship at theCrucible Theatre in Sheffield.
A director on World Snooker's board since 2006, the Scot said: "I feel that my current position is untenable given that I am completely opposed to the proposals Barry Hearn has laid out, whereby the controlling rights in the company are handed over to him.
"I do understand what Barry is trying to achieve in snooker, and we have discussed this at considerable length, but on this one we agree to disagree
"Barry has always run his own business and made his own decisions.
"However, I feel extremely uncomfortable where, from my perspective, decisions are being taken on contracts without me being consulted as a board member.
"I do wish some of the players would look at these proposals from the business angle and see the bigger picture... rather than turning everything into some kind of popularity contest between those they like and those they don't want to listen to."
Hearn said: "I welcome Lee's decision to resign as a director of WPBSA.
"As a manager of players and promoter of rival events in important territories like China, his position as a board director, where confidential information becomes available to effectively a competitor, has become untenable.
"I'm glad to say that the remaining board members - Steve Davis, Brandon Parker and Pat Mooney -are, like me, totally committed in supporting these new proposals for taking the game forward and look forward to discussing them with the players."
Hearn's proposals also include plans for an extended professional tour and a golf-style qualifying school for the main tour