Those working in the hospitality industry and those who've changed their work circumstances are among most at risk of having their holiday pay calculated incorrectly.
It's a headache which has dogged employers for years, with some blaming the complex Holidays Act, but has only recently come to prominence with a number of large businesses and government departments who've come across the problem.
How is holiday pay calculated?
Around 1700 hospitality businesses have contacted Hospitality NZ with holiday pay problems.
E tu union says the hospitality industry has many young workers with a lot of flexible hours.
"In all those areas where there are casual, temporary, precarious work of any nature, that people will be very vulnerable," spokesperson Ged O'Connell says.
Small business could also be vulnerable to having calculated the pay wrong.
So what can employers and employees do if they think they've got a problem?