Notwithstanding section 1321.31 of the Revised Code, no assignment of, or order for wages or salary is valid unless the wages assigned or ordered are to be paid for the support of the employee’s spouse or minor child in complying with an order of a court of record for the support of the employee’s spouse or minor child. This section does not affect or invalidate any contract or agreement between employers and their employees, or as between employers, employees, and any labor union as to any checkoff on the wages of such employees as may be agreed upon. This section and section 4113.16 of the Revised Code shall not affect or invalidate any deduction from the wages or salary made in accordance with a payroll deduction plan agreed upon between the employer and employee provided that the same be revocable at any time by the employee upon notice to the employer up to the time of payment thereof.