Commission wages paid to any person employed by an employer licensed as a vehicle dealer by the Department of Motor Vehicles are due and payable once during each calendar month on a day designated in advance by the employer as the regular payday. Commission wages are compensation paid to any person for services rendered in the sale of such employer’s property or services and based proportionately upon the amount or value thereof.

The provisions of this section shall not apply if there exists a collective bargaining agreement between the employer and his employees which provides for the date on which wages shall be paid.