The sides meet at the Stade Auguste-Bonal on Ligue 1 on Saturday amid disagreement over a reported deal that would see Ayew ruled out against his parent club under the terms of his loan from Marseille.
According to Labrune, there is a gentleman's agreement in place that says Ayew cannot be selected for the fixture - something denied by Sochaux.
Labrune believes it could be an innocent mistake that coach Herve Renard was looking to select Ayew, who has scored one goal in 10 games since moving, but thinks it could also be bad faith.
"We were determined that he would not play against us if it was loaned," Labrune told L'Equipe.
"I learned that Herve Renard is not aware of it and that they will probably play him. This is at best a misunderstanding and at worst bad faith.
"I take note but it still breaks all the traditions and customs."
Sochaux president Laurent Pernet had said earlier this week that there was "no written agreement or gentleman's agreement" in relation to the matter.
"I'm perfectly calm. What bothers me is that our good faith could possibly be questioned," he added.
