When an Employer changes the working conditions by changing the rules of employment, if the Employer informs the Worker of the changed rules of employment, and if the change to the rules of employment is reasonable in light of the extent of the disadvantage to be incurred by the Worker, the need for changing the working conditions, the appropriateness of the contents of the changed rules of employment, the status of negotiations with a labor union or the like, or any other circumstances pertaining to the change to the rules of employment, the working conditions that constitute the contents of a labor contract are to be in accordance with such changed rules of employment; provided, however, that this does not apply to any portion of the labor contract which the Worker and the Employer have agreed on as being the working conditions that are not to be changed by any change to the rules of employment, except in cases that fall under Article 12.