Young expectant and new mothers need help to know their rights at work after a study found they were significantly more likely to suffer discrimination.
Six times as many under 25-year-olds reported being sacked after telling their employer they were pregnant than the average, according to the Equality and Human Rights Commission (EHRC).
Its research among 3,200 working mothers of young children found that those under the age of 25 were more likely to be discouraged from attending antenatal appointments, given unsuitable workloads or suffer from stress than other mothers.
Now a campaign is being launched to help such women learn about what is allowed.
About 6% of under-25s said they were dismissed after informing their employer of their pregnancy, compared with an average for all women of 1%.
Discrimination uncovered by the study included sackings for pregnancy-related sickness or simply for being pregnant, and not offering the same training or promotion opportunities.
A young mother who took part in the survey said there was no risk assessment of her job in a store, so she ended up in hospital after moving and lifting things.
Caroline Waters, deputy chairwoman of the EHRC, said: "Young working mothers are feeling the brunt of pregnancy and maternity discrimination with more than any other age group being forced out of their jobs, facing harassment and experiencing issues with their health as a result.
"Often these women aren't established in their careers, with junior or unstable roles, low paid and reliant on their wage to support themselves and their babies.
"They need the knowledge and confidence to raise issues with their employers so they can focus on their health and wellbeing, rather than the negative impacts of this discrimination.
"We cannot continue to allow these young women to be unfairly held back in the starting blocks of their working lives when they could have the potential to achieve greatness."
Carole Easton, chief executive of the Young Women's Trust, said: "Sadly it is not surprising that young women are those who face the greatest discrimination.
"The scale of the issue is however worrying. Although some employers will do better than others, we are no longer talking about isolated instances but an endemic problem that affects the health and long term prospects of women in most workplaces."
Amy Leversidge, employment relations advisor at the Royal College of Midwives, added: "It's very worrying that the cases of young 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."
Campaign information can be found on #PowertotheBump.
It will bring together young mothers to share their experiences and knowledge so they are able to assert their rights and challenge any poor treatment which might be discriminatory, and have an impact on themselves and their baby.
The campaign features a new video starring mum vloggers Katie Ellison, Jess Avery, Charlotte Louise Taylor and Emily Norris. It will be available here from late afternoon on May 17.