In a week when women's roles have been highlighted by the promotion to Cabinet of a number of Tory female ministers, Nick Clegg wants to enact a clause in the 2010 Equalities Bill, which was drafted by the previous Labour Government but never implemented.
Under the proposal, employers across the UK with more than 250 people would annually have to make public the average pay of their male and female employees, "creating pressure from staff and customers to account for and close any gap that exists," said a party spokesman.
Since the election the Coalition has encouraged leading employers to publish pay gap information on a voluntary basis but only 140 firms have done so.
The spokesman said that, while the Lib Dems had lobbied for more action within the Coalition, the Conservatives refused to act.
They believe it is now time to go further.
"Forty years after the Equal Pay Act was passed it is utterly unacceptable that women are not being equally rewarded in the workplace, with women paid, on average, 20 per cent less than men," declared Mr Clegg. "Real equality means fair pay. It's time to accept the voluntary approach does not go far or fast enough.
"We need to lift the lid on what big companies pay the men and women they employ; with that information there for every employee and customer to see."
Jo Swinson, the Women and Equalities Minister, who represents East Dunbartonshire, added: "The Liberal Democrats have fought for shared parental leave, extra childcare, a new right to request flexible working, and we are determined to tackle the issue of gender pay.
"If women in the workplace are to have the same opportunities and choices as men, they must be properly rewarded for their talents and skills; it's as simple as that."
The party spokesman explained the new legal requirement would apply to just 7,500 large companies or 0.13 per cent of the total.
Yet, he noted, these firms collectively employ millions of people.
lThe Deputy Prime Minister hinted that he might be prepared to introduce all-women shortlists to boost the number of Lib Dem female candidates, saying that while the party was hoping to get more women MPs by giving them more support, if that did not work, then it might move to "what some regard as a more illiberal solution".
His words came as it emerged there are, among the 56 Liberal Democrat MPs, as many knighted males as there are women (seven).