Every employee must have a written employment agreement. It can be either an individual agreement or a collective agreement (one involving a union).
There are things that must be included in employment agreements by law. More information is available on the Ministry of Business, Innovation and Employment’s website which also has a free online employment agreement builder:
Minimum employment rights must be met regardless of whether or not they are included in an employment agreement or if the agreement states something less than a minimum entitlement.