At 11.59pm on Wednesday the deadline passes for UK companies to report their gender pay gap details to the government.
So far 78% of employers who have submitted their data have a gender pay gap, compared to 8% who have none and 14% who have one in favour of women.
Airline Ryanair is one of the worst offenders, with a median gender pay gap of 71.8%.
But what exactly is the gender pay gap, and what happens if companies miss the deadline? Here is everything you need to know.
What is the gender pay gap?
It is the difference between the average salaries of men and women in a given company or public body. It isn't the same as equal pay, where firms are required to pay men and women doing the same job the same salary.
A company may pay men and women in the same role the same wage but still have a gender pay gap, for example if most of their senior positions are filled by men who earn more.
Who has to report it?
Companies and public bodies with 250 employees or more are required to publish their data by April 4 and March 30 respectively, and submit it to the government Equalities Office.
It is estimated that around 9,000 employers will have to submit such information. So far more than 9,000 have done so, but without a full list of companies who are required to, it is not known how many are left to file reports.
Who are the best and worst so far?
NWN media, which owns a range of local newspapers, currently tops the table with a median gender pay gap of 85.2%.
Luxury skincare brand Elemis sits at the opposite end of the spectrum with a gap of 111.4% in favour of women.
Why has the UK government decided to do this?
When the requirement to report came into force in 2017, the government said closing work-related gender gaps could add £150 billion to the UK's annual GDP by 2025.
Minister for women and equalities at the time Justine Greening said: "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."
What happens when the deadline has passed?
The Equality and Human Rights Commission (EHRC), whose job it is to impose sanctions on non-complying firms, said it will write to employers who have not submitted their figures on April 9, giving them 28 days to do so "before an investigation takes place and an unlawful act notice is issued".
Those who report their figures within 28 calendar days of the EHRC's letter are expected to report on time next year to ensure no sanctions are applied.
Those who do not report their figures within the expected time frame will face investigation - if taken to court, an unlimited fine can be imposed.