The Government is being urged to conduct a "radical rethink" of legal protections for pregnant women and new mothers to stop many losing their jobs unfairly.
The Maternity Alliance said one in 20 new mothers will be made redundant during pregnancy, while on maternity leave or shortly after returning to work.
Rosalind Bragg, the charity's Director of Maternity Action, said some of the redundancies were discriminatory, and many were "completely unfair."
She added: "The current legal framework is not protecting women from unfair treatment. Women are being forced out of their jobs by redundancies which are not genuine and by discriminatory selection processes. Women who have challenged bad practice by their employers are at particular risk.
"We are calling for the UK to adopt the German model of redundancy protection for new mothers. Women should not be made redundant, except in limited circumstances, from notification of their pregnancy through to six months after return to work."
The charity said few women take legal action on discrimination, even when they have a very strong case.
A Business Department spokesman said: "Discrimination in the workplace is illegal in any form. We are considering ways of ensuring new and expectant mums feel properly supported and protected at work, including meeting with charities, employers and parents."