Early childhood teacher union The Educational Institute (NZEI) is launching a campaign for increased government funding for the sector today.
The NZEI said the quality of education was at risk because the amount that crèches and kindergartens received for each child had fallen in real terms.
NZEI president Louise Green said the government had been focused on increasing enrolments and now it was time to focus on quality.
She said in 2010 the government cut the subsidy rate that was paid to centres where all teachers were subsidised, and since then, early childhood subsidies have not kept up with inflation.
"Since 2010 we believe that there's been a cut - in real terms, that's about 5 percent - so that needs to be restored, plus compensation for what's happened over time," she said.
"These centres are really struggling and they need that funding restored."
Parent Amelia Handscomb was at the campaign launch, and said she had been on management committees at her children's early childhood centres, where they were finding it hard to make ends meet.
"That's creating a really pressured environment where some difficult decisions are having to be made around staffing numbers, around the group size of children and around the length of session hours," she said.
"These decisions are not really around the best interests of children, but are around surviving in this climate."
Ms Handscomb said early childhood centres had been struggling for several years, but it could not go on indefinitely.
"The question is how sustainable is this. How much longer can we sustain this increased effort, increased volunteer hours from parents, and low wages or less staff?"
'It has such an effect on our health'
Teacher Andrea Shepherd said teachers knew their centres were struggling so they helped out by giving up things like non-contact time or time in lieu.
She said quality had not yet suffered.
"We make sacrifices to keep it high, and I think that's why educators like me are speaking up now because we can't maintain that. It has such an effect on our health."
Ms Shepherd said the government needed to increase per-child funding and also reintroduce the higher funding rate for centres where all teachers are qualified and registered.
"We need the financial commitment to having 100 percent qualified teachers again, because this is where high-quality centres like this, which run at 100 percent, take such a financial hit for that decision."
Education Minister Hekia Parata said the government had doubled its spending on early childhood education since 2007 and the percentage of qualified teachers had increased since then.
"There are around 25,000 staff working in early childhood services across the country. Around 74.6 percent of those are qualified teachers, which has increased from around 61.1 percent in 2008," she said.
Ms Parata said the government spent more than $1.6 billion a year on early childhood education and for every $1 parents contributed, the government spent $4.80.
She said early childhood education was 33 percent more affordable than it was in June 2007 and the number of early childhood centres failing Education Review Office reviews had fallen from 28.8 percent in 2008 to just 2.6 percent in 2015.
Education impacted as funding eroded - early childhood groups
But other early childhood groups agreed with the NZEI that funding had eroded on a per-child basis.
Early Childhood New Zealand chief executive Kathy Wolfe said the decrease had hurt the quality of education.
"The quality's been eroded because some centres are either choosing to cut back the hours of the qualified teachers or to bring in unqualified teachers," she said.
"What they're trying to avoid is actually increasing the fees for early childhood services because at some point there's going to be a tipping point in terms of parents being able to afford it."
The Early Childhood Council said the government had been cutting the sector's funding in ways that were not obvious to the public.
They included childcare subsidies increases that did not keep up with inflation, cutting the subsidy rate for centres where all teachers were registered, and withdrawing funding to help centres coach newly qualified teachers toward full registration.
It said the cumulative impacts of the cuts cost the average centre more than $90,000 a year.