“To preserve discipline and competition, and to prevent the enticement of players, coaches, managers and umpires, there shall be no negotiations or dealings respecting employment, either present or prospective, between any player, coach or manager and any Major or Minor League Club other than the Club with which the player is under contract, or acceptance of terms, or by which the player is reserved or which has the player on its Negotiation List, or between any umpire and any baseball employer other than the baseball employer with which the umpire is under contract, or acceptance of terms, unless the Club or baseball employer with which the person is connected shall have, in writing, expressly authorized such negotiations or dealings prior to their commencement.”