Unlawful wage discrimination may be more widespread than previously feared, as equal pay remains a “distant dream” for many women, a new study suggests.

The Fawcett Society said three out of five women either don’t know what their male colleagues earn, or believe they are paid less for doing the same job.

Only two out of five of 1,000 women surveyed for the campaign group said they knew they were being paid the same as male colleagues.

The report was published to mark Equal Pay Day – when women are said to effectively start to work for free for the rest of the year because of the gender pay gap.

Two thirds of women polled said finding out they were paid less than men had a detrimental impact on how they feel about their employer, with some wanting to look for another job.

The survey also suggested that around two out of five women felt undervalued, angry and upset, with fewer than one in four saying they understood why there was a pay difference.

Sam Smethers, Fawcett Society chief executive, said: “Nearly 50 years on from the Equal Pay Act, equal pay for equal work is still a distant dream for many women. Pay secrecy means women cannot know if they are being paid equally and fairly.

“Even if they do suspect a man is earning more it is almost impossible to do anything about it. This is why we are calling for a change in the law. Women need an enforceable right to know what their colleagues earn so that they can challenge unequal pay.

“Men can help by simply telling their female colleagues what they earn.  It really is that simple.

“This is about much more than money. Women have told us they felt furious, devastated, exploited and undervalued. Pay discrimination has a significant negative impact on how they feel about their employer.

“A right to know will also reduce waste in the court system, and head off legal action by encouraging employers to settle cases before they get to court.”

TUC General Secretary Frances O’Grady said: “Today’s the day when women effectively stop getting paid for the rest of the year compared to men. Working women deserve so much better.

“The next government must deliver real change for women. We want tougher employer action to close the gender pay gap, flexible work from the first day in the job, better maternity and paternity pay, a new law to prevent sexual harassment and new laws to end pregnancy and maternity discrimination.”

Young Women’s Trust chief executive Sophie Walker commented:  “Today is the day we all talk about closing the pay gap, but our research reveals half of all working mums aged 18-30 skip meals at least once a week because they struggle to balance just getting to work against the cost, inflexibility and inaccessibility of childcare.

“We’re a long way off dealing with the basic problem of access to paid work, which is the foundation of access to equal pay.”

Charlotte Woodworth, of Business in the Community, said: “Each year, Equal Pay Day comes around far too early. Rather than closing the gap, this year the difference in men and women’s pay has widened for the first time in six years.”