Section 18
SEC. 18. Every order of the Board shall be served upon every public-service corporation to be affected thereby, either by personnel delivery of a certified copy thereof or by mailing to any one of the principal officers or agents of the public-service corporation, at his usual place of business, a copy thereof; and, in case such certified copy is sent by registered mail, the registry mail receipt shall be prima facie evidence of the receipt of such order by the public-service corporation in due curse of mail. The Board shall be authorized to suspend or modify its orders upon such notice and in such manner as it shall deem proper. It shall be the duty of every public-service corporation, its agents and employees, to observe and comply with such orders so long as the same shall remain in effect.