Six times as many mothers under 25 reported that they were dismissed after informing their employer of their pregnancy compared to older mothers, the Equality and Human Rights Commission (EHRC) found.
In addition, 13% of mothers under 25 reported being so poorly treated that they felt they had to leave their job.
In response to the statistics, the EHRC has launched #PowertotheBump, a digital campaign to help young, expectant and new mothers know their rights at work and have the confidence to stand up for them.
"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," Caroline Waters, deputy chair of the Equality and Human Rights Commission said.
"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," Waters continued.
The research from EHRC was commissioned in partnership with the Department for Business, Innovation and Skills. Research company IFF Research Ltd interviewed 3,254 mothers with a child under two and 3,034 workplaces across the UK.
One in 10 mothers under 25 (10%) reported they left their employers as a result of risks not being resolved, compared to an average of 4% among mothers of all ages.
Twice as many mothers under 25 reported feeling under pressure to hand their notice in on becoming pregnant compared to the average. And 15% of mothers under 25 said they were discouraged from attending antenatal appointments, compared to the 10% average.
Examples of discrimination under 25s cited included: not being offered the same training or promotion opportunities; being dismissed because of pregnancy-related sickness; and being refused time off for ante-natal appointments.
Siobhan Freegard, founder of the video parenting site Channel Mum said the figures are "worrying".
"It's a very worrying fact that young mums are more likely to face maternity discrimination and be forced out of a job - but are least able to cope with the consequences," she told The Huffington Post UK.
"They are often less established in their careers, earning a lower wage and with less awareness of their rights. Many will be in rented accommodation and may even face losing their homes without a job.
"Many young mums report feeling belittled at work with colleagues asking if their baby 'was an accident' and mocking how they are going to cope.
"But in a world where we want youngsters to take more responsibility, young mothers who want to work and pay their way should be supported, not have barriers forced in their way."
Using social media communities, #PowertotheBump hopes to bring together young mothers sharing their experiences online.
As part of the #PowertotheBump campaign, the EHRC has released advice for young mothers.
#PowertotheBump tips for young mothers
1) Talk to your boss
It is good to have early conversations with your line manager.
2) Attend your antenatal appointments
You are entitled to take reasonable paid time off during working hours for antenatal care. You should be given the time to travel to the appointment or class.
3) Plan your maternity leave
The most important thing is to keep talking with work, tell them your wishes and get it all agreed in writing so you feel in control. You need to tell work your maternity leave plans around the six-month mark - that’s 15 weeks before the baby is due.
4) Talk about health and safety risks
Always talk to work about any risks that are worrying you. Your employer has a duty to look after the health and safety of everyone at work. You can ask to see a copy of the general risk assessment to make sure you’re comfortable and safe and that any risks are resolved.
5) Reduce your stress
Don’t cause yourself additional stress. You shouldn’t experience a negative impact on your health and stress levels, be given an unsuitable workload or be treated unfavourably and feel less valued.
Waters added: "We want young women to use #PowertotheBump to speak up against this unfairness.
"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 Young Women’s Trust said it's "unsurprising" that young women are facing the greatest discrimination.
"Through our own work with young women who are struggling to live on low or no pay, we know many young mothers are afraid of speaking out about discrimination for fear of losing their job, and in too many cases are never made aware of their employment rights to start with," she said.
"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."
Rosalind Bragg, director of Maternity Action, said their advice line frequently receives calls from young women facing serious problems with their employers.
"They face a sudden drop in the number of shifts they are offered, unsafe working conditions, harassment and unfair dismissal," she explained.
"Pregnant women and new mothers have the right to a safe workplace which is free from discrimination.
"It is important that young women are supported to know their maternity rights and to take action when their employer breaks the law."