Some of New Zealand's biggest companies and several government departments are being investigated for possible payroll issues.

Labour Inspectorate documents released by the Council of Trade Unions show 25 companies that had been found to have short-changed staff.

They include Police, the Ministry of Business, Innovation and Employment, and several large private businesses such as Compass and Bunnings.

But the inspectorate also provided a list of 34 organisations that were also still under investigation.

It includes Government agencies like Auckland Council, the Department of Conservation, Landcorp, the Ministry of Social Development and the University of Otago.

It also includes private companies like Downer, NZ Post, Fairfax, Fonterra, The Warehouse and ANZ.