Which? has reported that card companies are increasing earnings using "dubious" sales practices and "unjustifiably" high charges.
Credit card companies make around £427 million a year by charging customers for late payment or going over credit limits, Which? calculated.
One person in four has been charged at least once in the last year for doing this, Which? found.
Malcolm Coles, editor of Which?, said: "The credit industry has an alarming number of tricks up its sleeve to wring every last penny it can out of its customers.
"Lenders seem to have no qualms about persuading people to take on more debt than they can afford and they'll carry on doing it as long as they can get away with it."To read more about credit cards, click here.
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