More than 10,000 companies have submitted their gender pay gap figures to the Government Equalities Office - but who are the worst offenders?
Here, the Press Association looks at the 10 companies with the highest median gender pay gaps.
From healthcare providers to a budget airline, all the companies in the top 10 pay women more than two-thirds less than their male counterparts on average.
1. NWN Media - 85.2%
North Wales News owns several local newspapers, and is itself owned by media company Newsquest. It runs papers such as the North Wales Chronicle, the Chester Standard and the Powys County Times.
The Press Association has contacted Newsquest for comment.
2. Millwall Holdings PLC - 80%
The parent company of Millwall FC, also based at The Den, Zampa Road, reported that 3% of women get bonuses compared to 29% of men, while women's median bonus pay was 99% lower than that of their male counterparts.
3. GoToDoc - 77.0%
GTD healthcare runs GP practices and provides urgent care and out-of-hours dental services in north-west England.
4. Boux Avenue - 75.7%
Boux Avenue is a women's underwear store, with retail chains across the country. All of the staff in its lower three pay quartiles are female, and in the highest pay range 91% of employees are women and 9% are men.
In its report, Boux Avenue said: "Due to the intimate nature of our products, we predominantly attract female colleagues to our stores and head office which has a direct impact on our statistics.
"The part-time working patterns within the stores are particularly appealing to female colleagues and these roles are paid on an hourly basis, whereas the small proportion of male employees are in salaried roles."
5. Fusion People - 73.3%
Fusion People is a recruitment firm working across different sectors including construction, property, engineering and finance.
In its report, the company said: "As we work predominantly in the construction and rail sectors, our market has been historically dominated by male workers due to the nature of the work.
"We have found that most of the jobs filled by females tend to be clerical and at a lower hourly pay rate."
6. Aaron Services - 73.0%
Aaron Services is a heating contractor operating in East Anglia and the Midlands.
7. Malling Health - 73.0%
Malling Health is a group of two GP surgeries in Kent, run by IMH Group, a network of primary care sites across the UK.
8. Ryanair - 71.8%
Ryanair has a pay gap much larger than its rivals - when comparing median hourly rates at the airline, for every £1 men earn, women earn just 28p.
It says the disparity is because of the number of UK pilots it employs - 546 are male and only eight are female.
9. Connells Survey and Valuation - 71.0%
Connells Group's surveying and valuation panel management company carries out a range of services including building surveys and home buyer reports.
10. Fosse Healthcare - 69.8%
A home care and healthcare service providor to the public and private sectors, Fosse Healthcare operates in the East Midlands.