Relatively few women reach the top ranks of financial firms
Men working in the UK's financial sector receive five times more in bonus payments than women, according to a survey of 44 leading companies.
On average, women earn £2,875 compared with £14,554 for men, the Equality and Human Rights Commission found.
Chairman Trevor Phillips said the sector must take action "to address this shocking disparity of rewards".
Equality Minister Harriet Harman said the government was introducing "tough new measures" to tackle the pay gap.
BBC business reporter Brian Milligan said the survey, commissioned by Ms Harman, was believed to provide the most accurate picture yet of pay differences within banks and insurance companies.
One of the main reasons for the vast difference in bonuses is that relatively few women reach the top ranks of financial firms where the biggest rewards are paid.
It comes on top of an average difference of 39% between men and women's basic salaries.
The EHRC said the gender divide was "entrenched" by recruitment patterns, with women starting at companies on lower salaries and then being left behind throughout their career.
The commission also said that just one in four of the firms surveyed was undertaking a pay audit to try to investigate whether they had a pay gap.
Mr Phillips encouraged more firms to follow the lead of the "enlightened few".
"For business to thrive in the new economy it simply can't afford to recruit and reward in the way it has done in the past," he said.
"By bringing down arbitrary barriers, and changing practices that, intentionally or not, inhibit women's success, financial firms have the chance to boost morale, bring on new talent, and maximise the potential of their existing employees."
As well as pay audits, the EHRC said companies should appoint a board member specifically to drive change on the issue.
Ms Harman, who is also minister for women, said: "We cannot tackle discrimination if it is hidden which is why I asked the commission to produce this report.
"Equality is vital, not only for individuals, but for the economy and society as a whole.
"Despite many actions taken by the government since 1997, inequality and discrimination still exist, which is why we are introducing tough new measures in our Equality Bill including gender pay reporting and proposals to ban secrecy clauses which are particularly prevalent in financial services."
John Cridland, deputy director general of business group the CBI, said parts of the financial services sector still had "some further distance to go" in terms of equality.
"But, as in many other areas of business, women applying for the top jobs need more flexibility with hours and childcare responsibilities," he added.
The role of women in the City will be the subject of a new inquiry launched by the Treasury Committee this autumn.
The 44 firms questioned in the survey employ almost 300,000 workers - about a fifth of the sector's workforce.
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