The figures only "scratch the surface of a wider problem" according to Labour Party women's affairs spokeswoman Sue Moroney.
Ms Moroney said pregnant women and mothers were one of the most vulnerable parts of the workforce and lodging a formal complaint about this type of sex discrimination was daunting. "It's not an easy thing to do so I would suggest the number of complainants who have made it that far are just the tip of the iceberg."
She received many complaints from woman who had requested part-time work on return from parental leave but were forced back into full-time jobs by inflexible employers.
The commission published Employers' Guidelines for the Prevention of Pregnancy Discrimination in 2002 because of the increasing number of complaints and inquiries from women and employers.
In the foreword, then Chief Commissioner Rosslyn Noonan said the HRC had been receiving complaints for almost 15 years from workers claiming they had been unfairly treated because of their pregnancies.
High-profile employment lawyer Mai Chen of Chen Palmer said she hid her pregnancy for five months because of the culture and attitudes towards child-bearing women in corporate society.
"When I got pregnant I did not want my competitors saying to my clients 'Oh she's pregnant so she's probably going to take off on you'.
"So I decided the better thing to do was to hide it. And I really regret the fact that I had to do that because I was quite sick through it."
A human rights advocate who once worked at the United Nations on discrimination against women, Ms Chen said there needed to be a culture change to stamp out discrimination.
"There are hundreds of women who have not returned to the workforce because of this problem and it's an enormous waste.
"I look forward to the time when society is changed so that we are able to allow women to go through those experiences without being damaged."
Galia BarHava-Monteith, a founding director of Professionelle Charitable Foundation, a group supporting working women, said discrimination against pregnant women and working mothers reflected bad management.
She said employers should plan for the woman's return, keep her involved in big changes including inviting her to training sessions, and plan for the transition back to work allowing for flexible hours.
New mum felt pressure to leave her job
When Nikki Collins became pregnant with her son Zac in 2010, she suffered from terrible morning sickness which lasted all day.
She persevered at her job in Christchurch despite being admitted to hospital.
Her boss, already a father himself and with a pregnant wife, was unsympathetic.
"He was the most unsupportive person and had a bad attitude, where he should have been understanding."
Miss Collins used all her sick and annual leave, delegated work to staff, did paperwork from home and reduced her hours from 50 to 30 a week to cope.
"I ended up taking maternity leave early, which he was happy with."
After Zac was born finances dictated that Miss Collins return to work when he was 3 months old.
"I wanted to increase my hours but when I asked for my old full-time job to come back into play he changed the hours from days to early starts and often late finishes including weekends, which I rarely worked before falling pregnant."
These were times Miss Collins did not have childcare available. "So I resigned and he paid me out and I left. I was never offered another role with the company with better hours. It was a take it or leave it situation."
Miss Collins said she was upset, deflated and angry at the outcome but didn't have the energy to make a formal complaint.
Now though, the 25-year-old has another full-time "dream" job with supportive colleagues and Zac, 2, is thriving at preschool.
"Looking back it was the best thing I have ever done. Employers with pregnant staff need to take the time to listen and put themselves in their employees' shoes for a day.
"Same goes for employers without kids. They have no idea what it's like and would want to give up after a week of what we do."
The law
* An employee returning from leave is entitled to the same role she had before.
* An employer must ensure returning workers are not given less substantial conditions.
* Employees cannot be dismissed because they take parental leave, unless there is good reason.
Source: Employers' Guidelines for the Prevention of Pregnancy Discrimination
