In any case in which the commission may hold a hearing it may, before or after such hearing, make such independent investigation as in its judgment the public good may require; provided, that, whenever such investigation shall disclose any facts which the commission shall intend to consider in making any decision or order, such facts shall be stated and made a part of the record, and any party whose rights may be affected shall be afforded a reasonable opportunity to be heard with reference thereto or in denial thereof.