The Government has launched a £1m investigation into the discrimination faced by women who are pregnant or on maternity leave.
More than 9,000 pregnancy discrimination claims have been brought against UK employers since 2007 and there is evidence that the recession has made discrimination by employers more common and increasingly blatant.
The research will be conducted by the Equality and Human Rights Commission (EHRC) and will be the first official study of the issue for a decade.
Mark Hammond, chief executive of the Equality and Human Rights Commission, said he was alarmed at evidence that mothers are still being forced out of jobs or passed over for promotion decades after gender discrimination was outlawed.
He said: :"It is very concerning that in 2013 a number of women are still being disadvantaged in the workplace just because they are pregnant.
"That would be unlawful discrimination and needs to be tackled.
"We will look at existing research, gather new evidence and carry out our expert analysis to establish the extent of the problem and advise on how best it can to be addressed."
Similar research carried out in 2004 found that half of all pregnant women in Britain experienced some form of disadvantage at work simply for being pregnant or taking maternity leave, with 30,000 women reporting being forced out of their jobs.
Minister for Women and Equalities, Maria Miller, said: "It's unacceptable. I am determined that we tackle these systemic problems which leave women feeling undervalued and penalised. We have made... significant changes to help women at work but there is more to do."
One in 10 calls to the charity Working Families is now to do with discrimination over pregnancy and the charity has reported high numbers of calls on the issue for three years in a row. Around one in 20 cases handled by the Equality Advisory and Support Service is from someone contacting them about pregnancy discrimination.
Labour's Shadow Minister for Women and Equalities Gloria De Piero said: "We have been calling on the Government for months to properly investigate the extent of pregnancy discrimination, so this is welcome news. It is shocking that three years after Labour made pregnancy discrimination illegal, so many women are still losing their jobs or [being] sidelined after taking maternity leave.
"But Maria Miller needs to wake up to the impact her own Government's policies too. Low-paid new mums have lost almost £3,000 in support in the first two years of their baby's life under this Government and by introducing £1,200 tribunal fees, costing the equivalent of nine weeks maternity pay, challenging maternity discrimination has simply become unaffordable for new parents."
The announcement comes after David Cameron appeared to misunderstand pregnancy discrimination law in an answer in Prime Minister's Questions last week. He was asked by Diana Johnson MP if he thought it was fair "that a sacked pregnant woman will now have to pay £1,200 to take a maternity discrimination case to an employment tribunal?"
As part of his reply he said: "One thing that we have done is ensure that people do not earn such rights until they have worked for a business for two years." But Ms Johnson has since pointed out in a letter that pregnancy discrimination rights are not dependent on your length of service.
An education campaign aimed at employees and employers will also be organised by EHRC to raise awareness of discrimination rights and obligations when it comes to pregnancy and maternity.
A recent study by the Office for National Statistics charting changes to the workplace over the last 40 years showed that young women starting their careers are now just as likely to be in the top pay bracket for their age as their male counterparts.
But by the time they reach 30 – now the average age for having children – a gap between the numbers of men and women at the top of most professions opens and is not reversed later in life.
It found that although almost 200,000 married or cohabiting mothers had gone back to work in the last two years – the biggest such increase in a generation – they then face settling for lower wages and lower status than their male colleagues.
More on Parentdish: Maternity leave - your rights explained
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