But Education Review Office figures showed that while kindergarten gets better reviews, there was little difference between community-based and private educare centres.
In calling for an inquiry, NZEI national president Louise Green said there was no evidence that market forces provide quality education in the compulsory public education sector, but the Government refused to step in.
Labour education spokesman Chris Hipkins backed an inquiry, saying leaving it to the market was "irresponsible".
"[Early childhood providers] receive hundreds of millions of dollars in taxpayer subsidies every year. That's money that should be going into quality education and yet increasingly it's being diverted to shareholder dividends," Mr Hipkins said.
Green MP Catherine Delahunty said there needed to be a plan so that quality centres were in the right places.
Education Minister Hekia Parata said New Zealand had always had a mix of early childhood education providers.
"The Government does not dictate whether they should be privately or community owned. Its interest is the quality of the service provided, not who owns it."
Members of a 2011 taskforce and two subsequent sector advisory groups said they still had concerns but weren't sure an inquiry was best.
The groups recommended a long list of changes, most of which are yet to be fully addressed.
"We got very little response to those two working groups," said Nancy Bell, the head of Te Rito Maioha Early Childhood NZ.
She said although ERO and the ministry were now working together more closely, they had hoped for better regulation around group sizes, ratios and teacher qualifications.