Children at numerous Victorian childcare centres have been sent home early, as more than 100 childcare workers walked off the job.
Workers rallied across the state on Thursday, coinciding with Equal Pay Day, campaigning for better pay.
They're calling for a rise in wages to meet what other educators receive.
"The work we do is just as important as our colleagues in primary and secondary education, and it's time this is reflected in our pay," Melbourne childcare worker Rukmini Bose-Rahman said in a statement.
Workers are paid around $20 an hour or $40,731 a year. A classroom teacher in Victoria is paid $63,356 a year.
United Voice, the childcare industry union, says more walk-outs are expected if the pay issue isn't resolved.
"This is really just the beginning," state secretary Jess Walsh told AAP.
The union has commenced a case that will be heard by the Fair Work Commission.
During the 2016 election campaign, Opposition Leader Bill Shorten committed to support childcare workers in their case.
Parents were notified of the walk-outs in advance, with some of them joining the workers in their protests on Thursday.
"Parents are overwhelmingly supportive because they understand the work and value probably more than anyone," Ms Walsh said.
United Voice national secretary Jo-anne Schofield put the underpayment down to the industry's gender make-up.
"Educators are among the lowest-paid professionals in Australia for one simple reason - this workforce is 95 per cent female, and their profession is shamefully underpaid," she said in a statement.
Victorian Minister for Women, Fiona Richardson said the government is working on putting gender equality at the centre of workplace reforms, including increasing fully flexible jobs and introducing a minimum standard of gender neutral paid parental leave.
"Ending the wages gap is one of the many steps towards building a culture of respect towards women that will help build a society of equality and bring down the rates of violence against them," she said on Thursday.
