Thousands of employers 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."
Sarah Champion, shadow secretary of state for women and equalities, said: "It is shameful that it's taken the Tories seven years to bring into force this piece of equality legislation that Labour introduced in 2010.
"It is disappointing the new reporting scheme has no enforcement system or sanctions for those employers who refuse to publish their pay gap data.
"The Government has admitted that they do not have the ability, or intention, to identify employers who do not comply.
"Without ensuring compliance, this new reporting system could prove toothless."