A committee of MPs are calling on the government to take greater action to tackle the "motherhood penalty", which sees women and mothers paid less than men.
The Women and Equalities Select Committee said the government has failed to close the gender pay gap, warning that the economy is not growing as fast as it could as a result.
MPs said factors like lower part-time pay and a disproportionate responsibility for childcare were costing the UK economy around 2% of GDP, equivalent to £36 billion a year.
In November, the Office for National Statistics (ONS) said the gender pay gap was at its lowest since records began at 9.4%. However, it added that the gap had barely closed over the previous four years.
The committee's report said that providing support to help both women and men take equal responsibility for childcare "is one of the most effective policy levers in reducing the gender pay gap". It recommended giving new fathers and second parents three months, well-paid leave to encourage a better-shared childcare responsibility.
Maria Miller, chair of the committee, said: "The gender pay gap is holding back women and that isn't going to change unless the government changes its policies now.
"The pay gap represents a massive loss to the UK's economy and we must address it in the face of an ageing workforce, a skills crisis and the need for a more competitive economy."
Sarah Jackson, chief executive of the charity Working Families, said: "The 'motherhood penalty' is a price that women continue to pay at work and at home. The answer lies with fathers.
"A decent period of paid paternity leave would allow more fathers to care for their young children and push this out of the domain of 'women's work' for good."