Trade unions and women's rights groups are calling on the government to take drastic action against unequal pay this morning.
Concern is rising among equality activists about the slow pace of change on the issue. The government has been reviewing laws on equal pay for three years now, but the Tories and Lib Dems have already revealed their proposals.
An open letter has sent to the government from the Fawcett Society, Unite, the GMB and Unison, among others urging action on the issue.
Katherine Rake, director of the Fawcett Society, said: "This letter demonstrates the rising tide of concern amongst unions and equality charities about the slow pace of progress towards equal pay for women.
"At the next election, women will be looking to assess parties' commitment to this touchstone issue and there are likely to be political consequences for a failure to act decisively.
"The Tories and Liberal Democrats have already announced proposals for badly needed reforms to our outdated legislation."
On average women in the UK earn £4,000 less a year than men, but equality groups claim unlocking women's economic potential could contribute 1.3 to two per cent of GDP
The government is currently putting together a single equality bill, which would amalgamate and consolidate all previous equality legislation.