Labor is urging the government to enforce existing childcare guidelines to make sure children whose parents both work get priority access to places ahead of stay-at-home mothers.
Assistant Minister for Education Sussan Ley says she's heard from many frustrated parents who can't find a childcare place.
It's quite reasonable for working parents to expect to be able to access childcare that's affordable, near their home and offers work-life balance, the minister said.
The childcare rebate and benefit were aimed at getting more women into the workforce.
"But we're not really seeing the increase in workforce participation that we need to," Ms Ley said on Sunday.
Labor says there are already guidelines to ensure vulnerable children and those whose parents both work get priority access.
"If there is a problem where stay-at-home parents are getting access to childcare places ahead of working parents, it means the guidelines need to be enforced," early childhood spokeswoman Kate Ellis said.
She is concerned the government may be seeking to cut the amount of money available to subsidise childcare.
One of the issues is parents who don't work can get taxpayer subsidies for up to 24 hours of childcare a week.
The commission of audit recommended the government change this arrangement so no subsidies go to those who aren't working or studying.
The government is waiting on a draft Productivity Commission report into the entire childcare system, due at the end of July.
It could canvass the option of restricting the childcare benefit for non-working mothers.
Ms Ley wouldn't commit the government to a position, saying only she expected to get many policy ideas from the commission.
Early childhood union United Voice said childcare was chronically underfunded and the answer was to create more places where needed, not pitting parents against each other.