Thousands of workers in Doncaster are claiming Universal Credit as their low wages are not enough to live on.
Charities say that the "shocking" number of in-work applicants is due to low wages and housing costs.
According to Department for Work and Pensions figures, there were 3,985 employed claimants in Doncaster on Universal Credit in July 2018 - about 36 percent of the total.
Overall, there were 10,937 people on Universal Credit in Doncaster, 701 more than in the previous month.
Universal Credit is a new benefit, slowly being rolled out by the Government, which replaces six legacy benefits and merges them into one payment.
It includes income support, jobseeker's allowance, employment and support allowance, housing benefit, child tax credits, and working tax credits.
The idea of Universal Credit was to simplify the benefits system, however problems with its introduction have reportedly forced benefit claimants into hardship.
The plan was to roll it out by 2017, but a series of management failures meant the Government has put off the completion until 2023.
Pritie Billimoria, from Turn2us, a charity which helps people who are struggling financially, said it was “shocking" that such a high number of workers earn so little that they are forced to rely on benefits.
“Every day we hear from working people who are living hand to mouth and facing impossible decisions about whether to buy food or pay their rent.
“We know that the rise of in-work poverty and in-work claimants is complicated. Households are dealing with low pay, the rising cost of living and changes to welfare support, which are all having a compounding effect on the daily lives of families across the UK.
“Work needs to be a route out of poverty so people are not left dealing with the intolerable stress and anxiety that their wages don’t cover their basic costs of living.”
Katie Schmuecker, head of policy for the Joseph Rowntree Foundation, an independent social policy charity, said: “Low pay and high costs for housing and other essentials mean that for many, work is not providing enough to live on and the social security system needs to provide an anchor against being swept into poverty.
"As well as tackling the cost of living, the Government should act to restore the work allowance for claimants of Universal Credit so that people in work can keep more of what they earn."
By 2024, about 8.5 million people are due to receive Universal Credit, according to the DWP's estimates.
In July 2018, more than one million people were on this scheme in Britain - 59,000 more than in June.
Nationally, 37 percent of claimants were in work. Mid Sussex had the highest percentage of workers - 49.1 percent of the total. The lowest proportion was in Birmingham, with just 29 percent.