Almost 90 per cent of all Kiwi employers working in business report having no union members, according to a Government study of employers across the country.
One of New Zealand's biggest unions said this was "certainly disappointing".
The survey also shows that almost 20 per cent of all employers have undertaken a review to check if men and women in the same role were being paid equally.
The numbers are from the Ministry of Business, Innovation and Employment (MBIE)'s annual study of employer practices in New Zealand.
Almost 2400 small and large businesses were surveyed as part of the report.
It showed 87 per cent of employers reported that none of their employees were union members.
That number was 90 per cent for small businesses – firms with fewer than 20 employees – and 60 per cent for large businesses.
National's workplace relations spokesman Scott Simpson said while support for the union movement has been dwindling, the unions have remained a core element of the Labour Party.
"That explains why we're in the midst of the worst outbreak of strikes in decades."
Workplace relations Minister Iain-Lees Galloway deferred comment to the unions.
Council of Trade Unions (CTU) President Richard Wagstaff said the numbers were disappointing.
"We really believe working Kiwis would get a much better deal if they were united and empowered through belonging to their union."
He said the most common reason for people not joining unions was because people don't realise there is a union for them, or they don't know the benefit.
E tū Assistant National Secretary John Ryall said international experience shows that low level of union membership corresponds with the low level of collective bargaining.
MBIE's report shows employers with union members on staff were more likely to describe their current relationship with unions as positive rather than negative.
The MBIE report showed that almost one in five employers had said they had undertaken reviews to check that men and women in the same role were paid equally.
"However, few employers reported that the business had undertaken training about potential gender bias, 4 per cent, or sought advice regarding the Equal Pay Act 1972, 5 per cent."
Minister for Women Julie Anne Genter said it was encouraging that 20 per cent of employers were taking action to ensure women are paid fairly.
"There's obviously an opportunity for more employers to do the same," she said.
"Addressing potential gender bias means that everyone's talents can be fully utilised. This benefits everyone, especially business."
• An earlier version of this story wrongly said that 90 per cent of Kiwis working in business were not members of a union.
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