Section 8. The terms of the contract between a principal and a sales representative shall determine when a commission shall be due. If the time when such commission shall be due is not specified in a contract, the past practices between the parties shall control or, if there are no such past practices, the custom and usage prevalent in the commonwealth for the business that is the subject of the relationship between the parties shall control. All commissions that are due at the time of termination of a contract between a sales representative and principal shall be paid within fourteen days after the date of termination. Commissions that become due after the termination date shall be paid within fourteen days after the date on which the commissions became due.