Women have half the pension savings of men in defined contribution (DC) schemes, according to a report co-sponsored by the Trades Congress Union (TUC).
The study, carried out by the Pensions Policy Institute (PPI), shows that, on average, women have £7,500 in savings compared to men who have £14,500.
In defined benefit (DB) schemes, women typically have £32,000 in savings, below the average of £43,400, whereas men have £62,900.
The report, The Under-pensioned 2016, also revealed differences in state pensions. Women on average receive £7,540 from the UK government a year, an equivalent of £145 a week. On the other hand, men get £10,088 per year, or £194 a week.
As well as women, the TUC noted "large pension disadvantages" for ethnic minority workers, carers and the self-employed.
Carers typically have just £5,800 in savings in DC schemes - 44.8% below the average. In DB schemes they have only £6,000 amassed, which is 86.2% below average.
An Indian worker has, on average, less than half (£22,100) the savings of a white worker (£45,500) in DB pensions.
Black pensioners receive £7,228 in state incomes. This is 16% less than the average and 20% less than their white counterparts, who get £9,048 from the government.
Self-employed workers have 4.8% less in DC savings (£10,000) and 12.7% in DB (£37,900) savings than average pensioner.
All the groups relate to the average pensioner, who has £10,500 in DC schemes and receives £8,632 per year in state pensions.
TUC general secretary Frances O'Grady said: "Everyone should have the chance of a decent retirement income, not just men in full-time employment.
"Women, carers and ethnic minority workers will continue to have a tough time in old age if swift action is not taken. We urgently need a debate on how unions, government and employers can work together to can build on the success of auto-enrolment."
According to the report, reasons for the disparities include workplace discrimination, job segregation and the lack of flexible working.
The document added that despite recent changes to state and workplace pensions, these divisions would remain unless the government takes further action.
Daniela Silcock, head of policy research at the PPI said the underlying causes of disparities could not be tackled solely through pensions policy.
She said: "They involve labour-market, social and regulatory issues related to inequalities experienced during working-life.
"Therefore, addressing ongoing differences in private pension income would involve a joint effort from government departments, employers, social services, regulatory bodies and community support groups."