Under the Employment Relations Act 1999, section 10 workers have the right to be accompanied at a disciplinary or grievance hearing by a companion of their choice from the following list. 

The companion Notes
A full-time trade union official There is no necessity for the employer to recognise the union in question
A lay trade union official The lay official must be reasonably certified by the union in writing as having experience of, or having received training in, acting as a worker's companion at such hearings
Another of the employer's workers The employer has no control over which of its other workers would be a suitable companion, although no worker is obliged to act as a companion if he or she does not wish to do so

Related quick reference items

Right to be accompanied at disciplinary and grievance hearings - meaning of disciplinary and grievance hearings
Right to be accompanied at disciplinary and grievance hearings - the role of the companion