The extension of maternity leave to 12 from 9 months could be threatening women's careers as employers think twice before hiring or promoting those of child-bearing age, an equalities watchdog said.
Extending the amount of time a woman can take off work after giving birth to each child could unintentionally make them less attractive to employers, the Equalities and Human Rights Commission said.
Chief Executive Nicola Brewer said the change had entrenched the assumption that only mothers bring up children.
She called for a more flexible approach, offering more parental rights and choice.
"There has been a sea-change on maternity leave and flexible work and we welcome that," she told The Times ahead of a public consultation.
"But the effect has been to reinforce some traditional patterns.
"We have come a long way, but after winning all these gains it is worth asking: are we still on the right track?
"The thing I worry about is that the current legislation and regulations have had the unintended consequences of making women a less attractive prospect to employers."
She told BBC radio: "We think that the focus should be on letting parents decide who takes parental leave after the first six months."
The commission's helpline had received calls from women who had lost their jobs after becoming pregnant, she told The Times.
Concerns were reinforced earlier this year, she added, when businessman Alan Sugar was reported as saying many employers discarded CVs of women of child-bearing age.
According to government figures, such women make up around one third of the entire British workforce.
At the moment, only nine months of maternity leave is paid, but this will rise to a year by the end of the current Parliament.
Fathers are currently allowed two weeks paternity leave
The Federation of Small Businesses said paternal rights were moving "too fast, too furious" and called for a "reality check".
"We have heard anecdotally there are some, a tiny proportion, of employers who say: 'I won't be employing a woman of child-bearing age' but to use this as an argument to level-up for men, we believe is too fast, too furious," its spokesman told BBC radio.
"We would like a pause on all this legislation."
