The number of men in low-paid part-time work has increased fourfold over the past 20 years.
New research by the Institute for Fiscal Studies has found that one in five low-paid men aged 25 to 55 now work part-time.
While 95% of top-earning men normally work full-time, 20% of the lowest paid now work part-time.
That means wage inequality for men has risen over two decades, but for women the opposite is the case.
More women have had a better education in recent years and more have moved into full-time jobs. As a result their pay has improved and they have had less incentive to leave the workforce.
However, the research does not reveal why increasing numbers of low-paid men are working part time.
Jonathan Cribb, senior research economist at the IFS and author of the report, said: "To understand the drivers of inequality in the UK it is vital to understand the growing association between low hourly wages and low hours of work among men."
There are two schools of thought about what might be happening. It may be that increasing numbers of men want to work part-time, although this seems unlikely.
The second theory is based on the sectors where these low-paid jobs are found.
Six in ten of them are in the retail, wholesale or hospitality sectors.
That might suggest men who previously worked in low-paid but secure, full-time jobs in sectors such as manufacturing have lost that type of employment.
Instead they have been forced into the traditionally poorly paid and less secure services sector of the economy.
Yet those are the sectors of the economy that traditionally have employed large numbers of poorly paid and part-time female workers.