Thousands of new mothers are being forced out of their jobs every year because of discrimination in the workplace, a new study has suggested.
A survey of over 3,200 women found that one in 10 had been dismissed, made compulsorily redundant or treated so poorly they had to quit their job.
The Equality and Human Rights Commission (EHRC) said its research suggested that around 54,000 new mothers were losing their jobs across Britain every year.
The research, carried out in partnership with the Business Department, also found that one in five new mothers experienced harassment or negative comments from their colleagues, employer or manager when pregnant or returning from maternity leave.
One in 10 said they were treated worse by their employer when they returned to work after having a baby, and 7% revealed they were put under pressure to hand in their notice.
When mothers were allowed to work flexibly, around half said they received fewer opportunities at work or felt their opinion was less valued.
One in 20 mothers said they received a cut in pay or bonus after returning to their job.
Thousands of employers were also surveyed, making it the largest of its kind according to the commission, with most managers saying they were firm supporters of female staff during and after their pregnancies.
Around four out of five employers said pregnant women and those returning from maternity leave were just as committed to their work as their colleagues;
Two thirds of employers said they do not think pregnancy puts an unreasonable cost burden on the workplace.
Caroline Waters, deputy chair of the EHRC, said: "This research reveals the worrying levels of discrimination and disadvantage at work that women still face today. Not only is discrimination unlawful, but it is also bad for business.
"That's why today we're launching a major initiative to bring this issue into the public eye, improve awareness of the law and work with business and other groups to find workable solutions."
TUC general secretary Frances O'Grady said: "This shocking report shows that many employers are in denial about the scale of pregnancy discrimination in their workplaces.
"Becoming pregnant should be one of the happiest times in a woman's life, not a period of anxiety and stress.
"These findings must not be swept under the carpet. The current culture of bullying, harassment and ill-treatment that many female workers experience must be consigned to the past.
"Today's report should also act as a wake-up call to ministers. If they want more employers to comply with the law they shouldn't be charging women up to £1,200 to pursue a pregnancy discrimination claim."
Justine Roberts, chief executive of Mumsnet said: "The scale of the discrimination revealed by this research is shocking, but sadly it comes as no surprise.
"Despite legislation designed to protect women from discrimination in the workplace, it's clear that in many cases, companies are simply not following the rules."
Cathy Warwick, chief executive of the Royal College of Midwives, said: "It is very disturbing that the rates of discrimination against pregnant women are so high. Discrimination at work can cause stress, anxiety and depression which can potentially have an impact on the health of the woman and her baby.
"It is very worrying that the cases of women being denied time off to attend antenatal care are increasing. Women who miss antenatal appointments miss out on essential screening tests and valuable advice around smoking and nutrition.
"Evidence shows that missing antenatal appointments can increase the risk of smaller babies, premature babies, miscarriages and still birth. This is particularly important for women with complex health needs.
"Government must act to ensure pregnant women are not denied their rights and they are not discriminated against. This can lead to costly implications for the NHS but most importantly it can have potentially devastating effects on the health of the woman and her baby."
A Government spokesperson said: "While the overall picture shows employers want to support women it is troubling to see that some are still facing problems at work. We will use this research and the full report, when it is published, to inform future policy making.
"The EHRC will be undertaking important work, including producing an employer toolkit which will help employers to better manage a member of staff's pregnancy. They will also raise awareness with employers on the best ways to support their staff."
Steve Williams of the conciliation service Acas, said: "It is clear from this valuable research that businesses need to treat all their workers fairly as this will help them stay within the law.
"We have published a new guide today on pregnancy and maternity discrimination. From next month we are also launching a series of equality guides to help employers and managers identify, tackle and prevent discrimination in the workplace."
Shadow women and equalities minister Gloria De Piero said: "These are truly shocking findings.
"Labour established laws to protect women in the workplace from being pushed out because they are pregnant or take maternity leave but this Government has made it harder for women who suffer discrimination to seek redress."