15. (1) Every written agreement, between a producer and a milk dealer respecting the price of a dairy product or any conditions relating to the sale or delivery of such a product shall take effect only after having been approved by an order of the Board in accordance with paragraph d of section 38.
(2) Failing a written agreement, any producer and any milk dealer to whom such producer sells or delivers a dairy product shall be presumed to have entered into a contract, in that respect, for an indeterminate period.Neither of the parties shall terminate such presumed contract or amend the same except:
(a) with the authorization of the Board or for a reason determined by it;
(b) for the non-execution of the obligations of either party; or
(c) by the consent of the contracting parties.