Citizens Advice said its survey of 6,000 people suggested those receiving universal credit were six times more likely to have stopped spending on broadband in the last 12 months than non-claimants.
They are concerned the problem could get worse, with people claiming the benefit four times more likely to be behind on broadband bills. The charity also said those struggling could have benefited from cheaper social tariffs or special low-cost packages.
According to Ofcom, one in three UK households had an issue affording their communication services. Watchdog Ofcom has also warned 4.3 million eligible people are missing the low-cost package deals.
The government said it had encouraged social tariff take-up by working with Ofcom and the industry to introduce a range of products to the market.
These were available in 99% of the UK and started from £10 per month, it added.
However, Ofcom found the take-up of social tariffs remained very low - at about 5% of those eligible - although it had quadrupled since January last year.
Dame Clare Moriarty, chief executive of Citizens Advice, said the watchdog needed to "hold firms' feet to the fire" to improve their take-up.
"People are being priced out of internet access at a worrying rate," she said. "Social tariffs should be the industry's safety net, but firms' current approach to providing and promoting them clearly isn't working.
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