Today marks Equal Pay Day, the day campaigners calculate that women start working for free when compared to male workers.
Women in full-time work earn on average 15% less than their male counterparts, according to Office of National statistics figures.
The gender pay gap has fallen steadily from around 20% at the turn of the century, but remains stubbornly high.
The gap is highest in the private sector, prompting fears that government cuts could widen the gap once more.
“As the age of austerity rolls on, the gap between women and men’s wages could well widen," Charlie Woodworth of the Fawcett Society said.
"With a million public sector jobs set to go in the next few years, the average gap in pay could widen as women take up lower paid work in the private sector."
George Osborne and equalities minister Maria Miller will today host senior business leaders at an event at Downing Street in an attempt to encourage more flexible working and paternity leave.
However Labour say the government are failing to do enough to tackle unequal pay.
"It is simply not good enough that forty 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," Labour’s shadow minister for women and equalities, Gloria De Piero said.
"On David Cameron’s watch decades of progress for women is slipping backwards."
Union leaders say woman are losing thousands of pounds a year due to a failure to bridge the gap.
"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," TUC general secretary Frances O'Grady said.
"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."