18. Service of summons or notice
Subject to the provisions contained in rule 20, an notice, summons, process or order issued by a Board, court, Labor Court, Tribunal, National Tribunal or an arbitrator empowered to issue such notice, summons, process or order, may be served either personally or by registered post and in the event of refusal by the party concerned to accept the said notice, summons, process or order, the same shall be sent again under certificate of posting.