Women professionals in some industries are earning £16,000 less than their male counterparts, according to a new report.
In the health service, the gender pay gap among professionals is three times greater than the average difference of around £5,000, the study by the TUC has found.
The research is published to mark Equal Pay Day - the point in the year at which campaigners say women effectively stop being paid because they earn on average 15% less than men.
Women working in the private sector fare worse than those in the public sector – a 19.9% gap compared to a 13.6% gap.
And the difference is greater for women working part-time, where the gap is 35%.
TUC General Secretary Frances O'Grady said: "It is a huge injustice that women are still earning on average almost £5,000 a year less than men. This pay gap can add up to hundreds of thousands over the course of a woman's career.
"The gender pay gap, which continues despite decades of girls outperforming boys at school and university, is also a huge economic failure. It is crazy that employers are missing out on billions of pounds worth of women's talent, skills and experience every year."
Gloria De Piero, Labour's shadow minister for women and equalities, said: "It is simply not good enough that 40 years after the Equal Pay Act women still don't earn equal pay for equal work, and despite doing better at school and university more women end up in lower skilled and lower paid jobs than men.
"On David Cameron's watch decades of progress for women is slipping backwards. With unemployment amongst women reaching its highest levels for a generation, and women paying three times more than men to bring down the deficit we need a Government that will deliver a recovery not just for a few at the top but one that works for women."
It comes as a separate study shows that women are not taking on management positions because of "masculine" workplaces and lack of flexibility from employers.
Some 60% of junior managers are female, but the figure is just 20% among senior staff, according to the Chartered Management Institute (CMI).
One of the problems is women's tendency to apologise more often than men - sometimes referred to as "sorry skirts", said the report.
Ann Francke, the CMI's chief executive, said: "Rather than a pipeline, we've had a female management pyramid for too long and it is time for change. Businesses need to support women to be authentic, individual and assertive, without becoming a cultural clone in a macho male environment.
"For years we've used the phrase 'glass ceiling' for women at the top, but more and more we find other obstacles, even at entry level, through middle management and beyond."