Women earn 43% less than men on average at accountancy firm Deloitte, updated figures have shown.
The figure takes into account the earnings of those at the top of the business - the partners - who are predominantly male.
The accountancy giant said that it paid men and women in the same roles equally.
All firms with more than 250 employees are required to report gender pay gap figures by 4 April.
But government guidelines say that partners in firms, which include accountancy and law firms, do not have to be included in this data.
This is because partners take a share of the profits rather than being directly paid by the companies.
Deloitte is the second of the big four accountancy firms to report updated figures. EY was the first of the big four to publish figures which took the earnings of its partners into account.
Deloitte said that its mean average pay gap was 43.2%, up from 18.2% figure it reported in July. But its median pay gap figure was 15.2%, down from 15.3% in October.
The jump in the mean figure is due to the addition of a relatively small number of very highly paid partners, which does not affect the median measure.
At Deloitte, 19% of the partners are women. The firm is trying to push this figure up to 25% by 2020.
Big accountancy and law firms have been under political pressure to publish updated figures.
This week, the chair of the Treasury Committee, Nicky Morgan, objected to firms using the "loophole" of not reporting the earnings of partners.
However, big accountancy firms say they have started including partner earnings voluntarily in gender pay reporting.
David Sproul, senior partner and chief executive of Deloitte UK, said: "Our role in society means we have a responsibility to lead on critical issues such as inclusion and diversity.
"Going forward, we commit not only to publishing the data required by the gender pay legislation, but also to publishing our gender earnings gap on an annual basis."
'Action, not audits'
When EY included partners in its calculations, its mean pay gap rose to 38.1%, and its median to 19.5%. That was up from the mean of 19.7% and median of 14.8% when it published figures in October.
A spokeswoman for PwC said that it would be publishing its pay gap figures to include partners "within the next few days".
KPMG said it would also update its data to include partner earnings.
"We take this issue very seriously and are in the process of finalising our pay gap data. We will publish that information shortly," the KPMG spokesperson said.
Labour said it would force firms to take action to close gender pay gaps.
Dawn Butler, Labour's shadow minister for women and equalities, said: "It's time to close the gender pay gap once and for all. But to address these deep rooted inequalities, we need action, not just audits.
"The next Labour government will require all large employers to prove how they plan to tackle their gender pay gaps and prove they are equal pay employers."
In February, Barclays said its investment bank had a mean gender pay gap of 48% and a median gap of 43.5%, while its retail bank had a mean gap of 26% and a median gap of 14.2%.