Businesses would have to give women returning from maternity leave their old job back at part-time or reduced hours under a claim being lodged by the unions.
If the position no longer exists, they would have to provide new mothers with a job of equivalent status and pay.
The ACTU will on Monday lodge the submission with the Fair Work Commission, who are reviewing modern award agreements, saying their changes would give greater protection to more than four million Australians.
ACTU President Ged Kearney said the new measures could only be refused "on substantial business grounds".
The proposals would stop discrimination against new mothers, and increase women's workplace participation, she said.
"The ACTU claim recognises that all workplaces are different and doesn't dictate specific terms - instead it puts in place a process that requires employers to genuinely consider alternative work arrangements when women return to work," Ms Kearney said in a statement.
When asked about the ACTU submission, Employment Minister Eric Abetz said workplace conditions were a matter for the commission.
"Those matters should be determined by that commission after hearing all the arguments from the trade union movement and any counter-arguments that might be available from employers," he told reporters in Hobart.
"I have confidence they will come to an appropriate landing on those issues."
The Australian Greens backed the push for more family-friendly work conditions.
"Rigid hours make it impossible for people to get control over balancing work and home, especially when they have a new child," Greens employment spokesman Adam Bandt said.
But business said dictating how employers interacted with employees would do nothing to improve women's workplace participation.
Not all businesses could accommodate parents' requests for flexible working arrangements, the Australian Chamber of Commerce and Industry said.
"A union push to mandate that businesses offer flexible part-time job opportunities ignores the realities of small businesses and risks harming the very people it intends to help," ACCI boss Kate Carnell said.
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