New gender pay reporting regulations are now in force, meaning UK companies with 250 or more employees will now have to publish their gender pay gaps within the next year.
Public, private and voluntary sector firms are now all required to disclose average pay for men and women, including any bonuses.
Firms are required to publish a snapshot of their employee pay as at 5 April 2017 if they are a private business or charity, or 31 March 2017 if in the public sector.
Around half of the UK workforce will be affected by the new reporting rules, covering 9,000 employers and more than 15 million employees.
Currently, the UK gender pay gap stands at 18.1% for all workers, or 9.4% for full-time employees.
If employers do not comply by the April 2018 deadline, they will be contacted by the Equalities and Human Rights Commission.
Companies with significant gender pay gaps will be encouraged to publish an action plan alongside the figures, detailing the steps they plan to take to address the discrepancy.