The government has been urged to encourage well-paid part-time work in an effort to cut the gender pay gap and help alleviate child poverty.
The latest TUC analysis of pay found the pay gap for women trebles in their 30s, blamed on part on a so-called "motherhood penalty".
Women choosing to work part-time after childbirth are most affected by low pay, with a paucity of well-paid part-time jobs and wages 40 per cent below men's full-time pay.
Both the TUC and Fawcett Society have called on the government to address the lack of skilled, flexible roles but the equalities ministers has said the pay gap will be tackled through legislation.
The TUC's Closing the Gender Pay Gap report found the wage gap between men and women extends to 11.2 per cent for 30- to 39-year-olds, nearly treble the 3.3 per cent divide for workers in their 30s.
This has been attributed to women's overrepresentation in low-paid jobs such as cleaning and childcare, but also an undervaluing of women's skills and an "employment penalty" for mothers.
TUC general secretary Brendan Barber said: "We all expect our wages to increase as our careers progress. But women's wages start to stagnate as early as their 30s and many are paying an unacceptable penalty simply for having children.
"Despite girls outperforming boys at school and at university, too many employers are still failing to make use of women's skills. This waste of talent isn't just hurting their take home pay, it's harming the UK economy too."
As a result, women are twice as likely to be classed as poor than men and have an average of £85 a week less disposable income.
The TUC blames this in part on a lack of quality well-paid flexible work for women, with nearly half of all part-time jobs badly paid.
Nearly three-quarters of part-time workers are women while at 7.5 million the UK has one of the largest part-time workforces in Europe.
The TUC argues "poverty wages" for women affect the whole family.
"If the government is serious about ending child poverty, it must raise family income by creating better paid, quality part-time work Britain's 7.5 million part-time workers," Mr Barber said.
The IPPR thinktank has previously warned that most families in poverty now have a member in work, with child poverty in fact rising among working households.
Harriet Harman, minister for women, argues the gender pay gap has fallen under Labour, down from 17 per cent in 1997 to 12 per cent.
But she said the government would introduce "tough new measures" to tackle unequal pay through the forthcoming equalities bill.
"I just don't believe women are less committed, less hard-working or less able than men. So they shouldn't be paid less," Ms Harman said.
The Fawcett Society is campaigning for the government to end pay discrimination with "preventative and remedial" measures in the Single Equality Act. It argues all companies should be ordered to conduct a pay audit to identify unequal practice.
"UK women cannot afford to wait any longer," Kat Banyard, campaigns officer at Fawcett Society said. "We need action from government now."