Male workers are borrowing £381 on average every month just to make ends meet, £100 more than women, according to new research.
Unite said a survey of more than 2,000 adults revealed a "growing debt crisis", especially among men.
The position was worse among younger men in their 20s, who were borrowing on average almost £400 a month, said the union.
General secretary Len McCluskey said: "Falling living standards and Government austerity are forcing ordinary working people into the clutches of these legal loan sharks. Their eye-watering interest rates, up to 4,000% a year, are trapping people in a spiral of debt.
"Men are at the sharp end of this debt crisis as they turn to payday vultures to pay the bills, put food on the table and make ends meet.
"We need a cap to halt the vicious cycle of payday loan misery and stop a generation of young men and women falling into a lifetime of high interest debt."
The union urged support for a move by Lord Mitchell to cap payday lender interest rates.