Pregnancy is now the number one reason behind workplace discrimination complaints, overtaking disability and family responsibilities for the first time.
Of 235 complaints received by the FWO in 2012-13 pregnant women who felt they had been discriminated against at work accounted for 28 per cent, up dramatically from eight per cent in 2010-11.
Historically discrimination due to physical or mental disability has been the key gripe of complainants, but the most recent report has complaints of such nature taking up only 21 per cent of the total.
Eleven per cent of complaints came from workers who felt their family or carer responsibilities led to them being treated differently.
Pregnant women who claimed they had been subject to discriminatory behaviour dominated complaints over these groups for the first time.
In one case, a Melbourne retail assistant had her roster slashed from 27 hours per week to just seven after telling her boss she was pregnant, and was told to accept the change or resign.
After resigning in what the FWO found to be "constructive dismissal", where the employee resigns because their employer's behaviour has become so intolerable that the worker is left with no other choice, the company was made to take corrective actions after workplace laws were explained.
Under the Fair Work Act, it is unlawful to discriminate against employees on a range of grounds including pregnancy, race, sex, and disability.
The FWO annual report also said working parents faced discrimination beyond pregnancy, finding barriers to accessing leave, including parental and carer's leave, and difficulty with requesting and using flexible work arrangements.