You can legally drive in New Zealand for up to 12 months if you have a current driver’s licence or an International Driving Permit (along with the original current driver's license) in English.  

If the licence or permit is not in English, you must carry an accurate English translation.
A translation of your overseas licence or permit can be issued by:
 
  • A translator approved by the NZ Transport Agency
  • A diplomatic representative at a high commission, embassy or consulate; or
  • The authority that issued your overseas licence (an international driving permit may be acceptable as a translation)

If your clients are caught driving without an acceptable English translation or an IDP, they may be liable for an infringement fee of up to NZ$1,000 and may need to appear in court. They will also not be covered by insurance.