Do casual workers get holiday pay?

That is not correct. Casual employees are still employees, and the Holidays Act 2003 applies. If your work is genuinely so irregular that it is not possible to determine your entitlement in advance, your employment agreement can provide for holiday pay to be paid as a percentage, commonly eight percent of gross earnings, with each pay, but it must be clearly identified on your payslip. Otherwise, you accrue annual leave in the normal way. You are also entitled to public holiday pay and alternative holidays if you work on a day that would otherwise be a working day, and once you have been employed for six months you may be eligible for sick leave depending on your pattern of work. Check your written employment agreement and payslips, and raise any shortfall with your employer, or request help from MBIE.