In any proceedings under the Industrial Relations Act 1996 in which a document is required to be served on an industrial organisation within the meaning of that Act, service of the document must be effected--
(a) by serving it personally on the organisation's secretary or principal officer, or
(b) by leaving it at the organisation's registered office with a person who is apparently employed by the organisation, or
(c) by sending it by post, addressed to the organisation's secretary or principal officer--(i) to the organisation's address for service in the proceedings, or(ii) if it has no address for service in the proceedings, to the organisation's registered office.