Wilde Sapte will have to defend its 'poison pill' partnership clause in an arbitration hearing brought by partner Thomas McDonald before the Paris Bar in April.
The clause states that only one partner may leave the partnership every six months and under the terms McDonald faced up to two-and-a-half years before he could join his new firm White & Case.
McDonald's case is based on his unusual circumstances. He is a French- and US-qualified lawyer working for an English firm and registered at the Paris Bar.
It is thought that he is basing his case on the ethical rules of the Paris Bar, which state that a lawyer is a "free and independent spirit".
The arbitrator is former Herbert Smith partner Gerald Pointon, chosen by both sides for his knowledge of the Paris and London professions.
McDonald announced his intention to leave Wilde Sapte after the firm's merger negotiations with Arthur Andersen developed last year. Previously, he had been a partner at French firm SG Archibald, but left when it became Andersens' captive firm in Paris.
McDonald agreed to join the Paris office of White & Case before Andersen called off the deal with Wilde Sapte last June.
The future of the office's two other partners remains unclear. Richard Macklin and Olivier Tordjman were reported to have decided to leave the firm, but as yet neither has revealed where they
are going.
It is also unclear whether they are being held to the same contractual obligations as McDonald.
Neither Thomas McDonald or Steven Blakely, Wilde Sapte's managing partner, would comment.