Research by Melbourne academics shows widespread ignorance or contempt of the unpaid parental leave standard.
Since 1979, working women have had the right to 12 months unpaid maternity leave and a return to their job.
The guarantee is being undermined by employers who sack women or make them redundant while they are pregnant or on leave. Some sabotage their return to work by abolishing their job or offering an inferior one. RMIT senior research fellow Sara Charlesworth said some employers considered the legal entitlement an "optional extra".
"I think that things have worsened, and what we have assumed as an absolute right is no longer understood as that," she said.
"There needs to be some proper auditing and reinvigoration of information about this fundamental right."
Dr Charlesworth and Fiona Macdonald, of RMIT's Centre for Applied Social Research, used data from a Victorian employment rights legal centre to see if the guarantee was being breached.
In the year to April 2007, 440 women contacted the service about pregnancy-related work concerns. Most were employed on a permanent basis, many for six years or more with the same company, and many in professional roles.
They found 54 women lost their jobs during pregnancy, while a further 47 had no job to return to or were made redundant while on leave. Ten more women lost jobs on returning to work.
More than three-quarters of these had worked for their employer for at least 12 months, a condition of the guarantee.
A further 48 women were refused their original job on returning to work, with many offered a job with reduced pay, hours or conditions, often as a casual.
Dr Charlesworth, who will present the study to a conference at La Trobe University next week, said the Howard government's WorkChoices had made it harder for women to seek remedy.