The union representing public service workers is calling for the payroll problem uncovered in one of the Government's biggest ministries to be quickly resolved.
The Ministry of Business, Innovation and Employment (MBIE) discovered the holiday pay issue but there are fears it's just the tip of the iceberg.
It's suspected the problem stems from changes made to the Holidays Act in 2004, and Finance Minister Bill English says other public sector agencies, as well as private sector companies, may find they too have fallen short of their legal obligations.
The Public Service Association says hundreds of ministry staff could be out of pocket and it's taking the issue very seriously
"We understand many of our members at MBIE may be affected and we have already been talking with the ministry to help them resolve the payroll errors," said PSA national secretary Glenn Barclay.
"We urge MBIE to resolve this as quickly as possible."
It's about the way holiday pay has been calculated, and Mr English wants government agencies to go back and check they've got it right.
But the State Services Commission says it's been working with agencies for the past 12 months to "make them aware of potential issues relating to their compliance with the Holidays Act".
Most agencies assessed no or only minor issues, but the commission continues to monitor the situation and work with agencies as necessary, a spokesperson said.
Late last year police discovered their staff had been incorrectly paid since 2009.
The money owed - which totalled close to $40 million - related to holiday pay, as well as annual, sick and bereavement leave.
Economic Development Minister Steven Joyce, who oversees MBIE, says holiday pay calculations are "fiendishly difficult to get right".
"It's not an excuse, but it is an area of payroll which is quite challenging and a number of public and private agencies have had some difficulties over the years," he said.
MBIE employs more than 3000 people. It isn't known how many are affected.