Thousands of employers in the UK will have to publish gender figures for the first time from today under new measures aimed at closing the pay gap between men and women.
Firms employing at least 250 workers will have to give wage figures by April next year, with the regulations covering over 15 million employees.
The government said the UK was one of the first countries in the world to report on the gender pay gap, currently just over 18%.
Ministers said the new regulations will help firms take action to close the difference in the pay of male and female workers.
Minister for women and equalities Justine Greening said: "We have more women in work, more women-led businesses than ever before and the highest proportion of women on the boards of our biggest companies.
"This has helped us to narrow the gender pay gap to a record 18.1%, but we want to eliminate it completely.
"Helping women to reach their full potential isn't only the right thing to do, it makes good economic sense and is good for British business.
"I am proud that the UK is championing gender equality and now those employers that are leading the way will clearly stand out with these requirements."
Verity O'Keefe of the EEF manufacturers' group said: "The transparency this data will drive is important, but it must also be recognised that the simple snapshot it will provide may often hide a more complex picture.
"Manufacturers are likely to unearth some higher than average figures.
"However, this is not due to a lack of support for women in our sector, far from it.
"Manufacturers offer enhanced and competitive maternity pay and schemes, flexible working and structured career and training plans.
"Instead, the problem is at the grassroots. Just a handful of engineering apprentices and graduates are female."
Sam Smethers, chief executive of Fawcett Society, said: "This is the most significant legal change since the Equal Pay Act and we strongly welcome it."
The Chartered Management Institute said its research showed that four out of five managers had witnessed gender discrimination in their workplace in the past year.
Only two out of five challenged bias in decisions on pay.
Chief executive Ann Francke said: "We may live in more enlightened times but clearly we still have some way to go.
"Men and women have an equal role in creating a company culture that benefits all, so managers must call out any bad behaviour whenever they witness it."
Closing gender gap worth billions to economy - report
Closing Britain's pay gap could add £150bn to the country's annual gross domestic product by 2025, according to consulting firm McKinsey Global Institute.
Other countries to introduce mandatory gender pay gap reporting include Australia, which passed similar legislation in 2012, and Germany, where a forthcoming law will affect companies that have more than 500 employees.
The government said the new law was part of a longer term scheme to support women in the workplace, including investing £5m to help parents return to work, providing 30 hours of free childcare, and introducing shared parental leave.
Women's rights group Fawcett Society said they "strongly welcome" the gender pay gap reporting legislation.
"Employers should see it as an opportunity not a threat. Through gender pay gap reporting they can address the productivity gap and get the best person for the job at the right level," Sam Smethers, chief executive of Fawcett Society said in a statement.
