The national body for building cleaners has warned that changes to government contracts could lead to workers being paid less or losing their jobs.
Previously, only cleaning companies who are a member of the Building Services Contractors Association (BSC) have been employed at government buildings.
Those companies agreed to pay staff above minimum wage and other employment standards.
But last week the Labour minister Simon Bridges announced that cleaning services will no longer need to be members of BSC to contract to clean Government facilities.
"The findings show that the requirement has several negative implications, including that it acts as a barrier to some providers, and it is inconsistent with international and domestic procurement best practice," said Mr Bridges in a statement.
"While the requirement was intended to help improve conditions of workers in the cleaning industry, few, if any, benefits have been achieved."
The Building Services Contractors Association's president, Patrick Lee-Lo, disagreed, and said the changes will lead to undercutting.
"Their pricing is bound to be cheaper than a BSC member's price, and that's where it could get tricky" he said.
"The incoming contractor may not have allowed for the outgoing contractor's staff to be employed, and I think you'll start to see some situations where cleaners will actually lose their jobs."
A spokesperson for the Service and Food Workers Union, Jill Ovens, said the change was an attack on low income workers.
"Despite the cleaning contractors' organisation, the Property Services Council and Business NZ, the Council of Trade Unions and the SFWU supporting the retention of protections for these vulnerable workers, the Government has ignored their advice," said Ms Ovens.
"As with this week's amendment to the Minimum Wage Order, this Government seems intent on a race to the bottom in wage rates rather than adopting measures that could give workers, such as cleaners, a wage they could live on" she said.