Dozens of childcare centres will close mid-afternoon to support the national campaign, which is the largest walk-off by early childhood educators and follows a similar action held on Equal Pay Day last year.

Qualified early childhood educators earn as little as $20.61 an hour, about half the national average wage and significantly less than workers in male-dominated professions with comparable skills and qualifications.

Childcare union United Voice has a long-running wage case in the Fair Work Commission, arguing that the 97 per cent female workforce is under-paid for working in a "pink collar" sector.

"It's women's work and it's undervalued," the union's assistant national secretary, Helen Gibbons, said.

"Historically people who worked in the sector were seen as doing the job for the love of it. It does bring people enormous joy and satisfaction but love doesn't pay the bills."

Figures from the Workplace Gender Equality Agency show the national gender pay gap is 16.2 per cent, with female-dominated industries attracting lower wages than male-dominated industries.

A metal fitter and machinist with a certificate III qualification earns $37.89 per hour, for example, compared with the $20.61 earned by the certificate III qualified educator.

"They have smaller wages but they don't have smaller mortgages, they don't have smaller gas bills, they don't have smaller electricity bills," Ms Gibbons said.

"We can't continue to provide high-quality early education while paying people poverty wages."

Margaret Carey, director of the Clovelly Child Care Centre, which is taking part in Wednesday's action, said wages did not match workers' skills or their contribution to society and the economy.

"The skills, qualifications and professionalism you need to do your job has escalated but that's not reflected in the pay," she said.

"There are many people who think early childhood is not a profession and it's not providing education. That's a perception we want to change. Care is a large part of what we do but it doesn't diminish all the other aspects of our work."

University-qualified early childhood teacher Lucy Gosling spends her days teaching children everything from the correct pencil grip to negotiation skills, the ethics of sharing and the importance of showing respect for others.

"I love my job but I am never going to get a loan to buy a house in Sydney on my wage and that is a bit sad," she said.

Kirsty Rutherford, who has two children at the Clovelly Child Care Centre, is supporting the push for fairer pay.

"Their pay does not reflect the significance of their role in society and the importance of what they do for families," she said.

"Without them, parents could not go to work. They are absolutely critical. It's mind-blowing that they are paid so poorly yet, without them, the entire economy would collapse."

A skeleton staff will remain on duty at centres where parents are unable to collect their children early on Wednesday.