One in seven employers admit they would be reluctant to hire a woman who might have children, according to a new study.
A survey of 800 managers found that concern was more common among men (18%) than women (10%).
The Young Women's Trust said its research also showed that one in four organisations considered whether a woman was pregnant or had young children during decisions about career progression or promotion.
The charity pointed out that making such hiring or promotion decisions was illegal.
Young Women's Trust chief executive Dr Carole Easton said: "It's no wonder women are held back in the workplace when employers have such outdated, discriminatory views.
"It is employers and our economy that miss out on the talents of young women as a result. Young women who want to work are meanwhile struggling to make ends meet and finding themselves in debt.
"Employers should value young women's contributions to their workplaces and do more to accommodate them, including by offering more flexible and part-time working opportunities.
"It's not just employers who need to stop treating women as second class citizens. Society as a whole should support men to take an equal role in childcare. Until that happens, women will continue to face discrimination at work."
One in three employers surveyed said that men will never take an equal role in caring for children.
Maria Miller, who chairs the Women and Equalities Committee, said: "Despite it being illegal to make recruitment decisions based on assumptions about a woman's role in childcare, these figures show that there is still a huge problem with pregnancy and maternity discrimination.
"When the Committee looked at this issue over a year ago it was shocked by the extent of discrimination.
"Its report called on the Government to take further action to encourage wider compliance with the law by employers."