No assignment or pledge of wages, in any form, made or executed directly or collaterally in the payment of, or as security for, the purchase of or contract to purchase any goods, wares, or merchandise shall be valid against or binding upon any employer, or the wages of any employee in the hands of, or owing, or to become owing to such employee, unless the assignee or pledgee thereof shall, prior to the delivery of the goods, wares, or merchandise so purchased or prior to consummation of any contract to purchase the same, serve upon the employer of such assignor, or pledgor, a duly executed copy of such assignment, or pledge, or contract to purchase and obtain such employer's acceptance of notice thereof and agreement in writing to be bound by the terms of such assignment or pledge.