The number of men in low-paid part-time work has increased "dramatically" over the past 20 years, in contrast to those on higher wages, a study shows.
Around one in five 25 to 55-year-old men on low hourly wage rates now work part-time, compared with one in 20 for higher earners, said the Institute for Fiscal Studies.
Pay inequality among men has risen significantly as the wages of high earners have increased, while those on lower rates work fewer hours, research found.
In contrast, inequality in women's weekly pay has fallen following a reverse trend of fewer working part-time, said the IFS.
Jonathan Cribb, senior research economist at the IFS, said: "The number of low-wage men working part-time has increased sharply over the last 20 years.
"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."
Liberal Democrat business spokesman Don Foster said: "We must tackle unfairness and inequality wherever it is found, including the incredibly worrying rise in men being forced into low-paid, part-time work.
"For all the Government's talk about helping 'JAMs', it seems the rich are getting richer while those who struggle get left behind."