The scale of an issue with payrolls, where thousands have been underpaid, could be much larger than imagined, the Council of Trade Unions says.
Investigations by the Labour Inspectorate recently revealed about 24,000 public and private sector employees nationwide had been underpaid since 2012 in breaches of the Holidays Act.
The average underpayment for some businesses was up to $1800.
However, Council of Trade Unions president Richard Wagstaff suspected there were many more than 24,000 people who have been underpaid.
"I think it's probably a lot bigger than what was first imagined. That doesn't mean thousands of people are owed thousands and thousands of dollars, but we do think there have been some miscalculations...it has probably been going on for years."
The problem with payroll may have become bigger in recent years as peoples' work was increasingly irregular, with some employees often chopping and changing their hours week by week, he said.
Mr Wagstadd met with the Labour Inspectorate today. A lot of work was needed on the Holidays Act, he said.