An estimated 70,000 families will be unable to send their children to child care as early childhood workers stage industrial action.
More than 1000 centres will be partially or completely closed as early childhood educators stage rallies across the country on Wednesday.
The United Workers Union has called on the federal government to guarantee wage increases and implement major reforms.
Workers will rally across the capital cities and some regional centres.
Union early education director Helen Gibbons said the sector was in crisis as the industry struggled with a worker shortage.
"They're exhausted, they're sick of being undervalued, and they're calling for change," Ms Gibbons told AAP.
"We estimate that 70,000 children and families will be impacted by the shutdowns, which means that they're not attending early education.
"Families won't be surprised by that. Educators will have been talking to them for weeks and talking to them about making alternative arrangements or joining them on the rallies."
Ms Gibbons said workers needed a solid commitment from the federal government that wages would rise.
"They need to know what this government's plan is to fix their wages and give them a reason to stay in the sector, but also to reform the sector," she said.
"The federal government cannot deliver on its promise of more affordable and more accessible early education if there's no early educators."
The minimum wage for a childcare support worker begins at $21.85 an hour, which is $830 a week before tax.
Goodstart Early Learning expects workers from about 200 of its centres to attend rallies but plans to remain open.
"All of our centres will be open. We have been working with the union to make sure there are enough educators on hand to care for all the children who will be in our centres tomorrow," Goodstart's head of advocacy John Cherry told AAP.
"We know that a lot of parents have opted to pick up their children early so that more of the educators can attend their rallies. A lot of parents are very supportive."
Mr Cherry said Goodstart believed wages need to be increased, pointing to "a huge gap between what educators are paid in the early childhood sector and what they're paid in government schools."
G8 Education said the company was aware some workers would be taking part in the industrial action.
"We will support this where we can while ensuring continuity of service is maintained for our families," a spokesperson said.
The UWU describes the action as a "shut down" rather than a strike.
The federal government has flagged a review into pricing across the system.
