Workers are borrowing £660 a month to make ends meet, three times as much as a year ago, "shock" new figures have revealed.
A study by the Unite union showed the scale of reliance on payday loan companies.
Unite called for urgent action to restore incomes, and legislation to clamp down on subprime lenders.
A survey conducted by Mass1 of 4,087 Unite members last month showed people were borrowing £660 compared to £328 in September 2012.
The figure has more than trebled from the £200 being borrowed in March 2012.
Two thirds of those surveyed who borrowed said they run out of money by the third week after they are paid.
Unite has dubbed this 'Wonga week', saying it is the subprime sector that is benefiting greatest from people's hardship.
While the number resorting to payday lenders remains unchanged since 2012 at one in eight, the amount that workers are borrowing has soared.
Unite said this suggests that rather than turning to these lenders for short-term help, they are falling deeper into debt. One "grim" statistic is that 68% of users of payday lenders need to return again the following month.
Unite general secretary Len McCluskey said: "It is a tragic consequence of this Government's economic policy that those with the least are shouldering the biggest debt burden.
"Low wages and insecure employment are destroying incomes, forcing people to turn to payday lenders with their outrageous interest rates.
"This is a personal debt pile-up that cannot be ignored and certainly ought to correct overblown claims of economic recovery.
"No recovery can be built on hardship and misery. But this Government could arrest this debt spread quickly and easily. It must toughen up the regulations covering subprime lenders, which are the most relaxed in the western world.
"The country is suffering the biggest economic squeeze since the 1870s. It deserves better than madcap Wonganomics and policies that aid the rich and powerful, while nearly one million people have been out of work for more than a year, 1.5 million who work part-time want a full-time job and possibly some five million people are on insecure zero hour contracts earning as little as £500 per month.
"The Unite survey shows that those who are borrowing are now borrowing the equivalent of more than one week's average wage every month."
Unite described the survey's findings as "shocking" and will raise the issue at the TUC Congress in Bournemouth today.