Researchers found 51 per cent feel their employer’s and colleagues’ attitude towards them changed when they became pregnant, while two-thirds said things had been “difficult” for them since they returned from maternity leave.
Being overlooked for promotion and forced to watch more junior employees progress faster up the career ladder were common complaints.
Many women also said they felt that their views were not considered as important as those of staff without children, and that they often felt “left out”.
Nearly half of working mothers felt having children halted career progression, while a third described rising up the career ladder as a mother “impossible”.
The poll of 2,000 mothers commissioned by employment law specialists Slater & Gordon found four in ten do not feel they have the support of their bosses.
Kiran Daurka, a lawyer at Slater & Gordon, said: “Despite the equality legislation in place, attitudes and working practices continue to block women in achieving their career aspirations in the UK.
“This report shows that there are still negative perceptions of women with children and this kind of attitude is short-sighted and bad for business.
“Anecdotally, we hear of mothers complaining about being put on a ‘mummy track’ when back at work, and this research illustrates that this is a real experience for many women.
“I find it quite dispiriting to hear that more than a fifth of mothers feel that they need to prove themselves to their bosses following their return from having a baby.”
A quarter of mothers felt under pressure to return to work earlier than they wanted to.
Feelings of frustration or being left “out of the loop” were common, while a fifth said they definitely felt less valued. Three in ten felt their bosses saw being a mother as inconvenient, and the same number thought it had played a major part in them missing out on a promotion.
Some 43 per cent felt those younger and without children were prioritised in the workplace over themselves.
The most common attitudes mothers faced were other worker’s frustration at their part-time hours, not being included socially or in business-related matters and a general perception that their role was just a job now, rather than a career.
Alastair Pringle, Scotland director for the Equality and Human Rights Commission, said: “It’s certainly worrying that such a high number of women still feel that motherhood is holding them back in the workplace and that they believe they are being treated unfairly.
“Legal protections or not, employers need to realise that they are wasting valuable experience and talent when they sideline any section of the population.”
“There are legal protections in place. This means that an employee – whether they are pregnant or returning to work as a mother – should not be treated unfavourably.”