As per ers.govt.
nz:
Our employer is advising that we will have to take two weeks annual leave because there's not much work on and she wants to have the offices renovated. Can she do this?
Yes. Your employer is in fact entitled to do this under the provisions of the Holidays Act 1981 if:
1. you have been employed for at least a continuous 12 month period and therefore currently have an entitlement to all or part of your 3 week physical annual leave entitlement, and
2. your employer gives you at least 7 days notice under section 19 of the Act.
So, it looks like your employer doesn't have to agree to when you want to take leave.
It also has to do with keeping things balanced for the business and stuff.