A debt charity has warned that thousands of clients are being hit with unarranged overdraft penalty charges averaging £225 a year.
StepChange said almost two-thirds of people seeking its help with overdraft debts (62%) had regularly exceeded their limit and faced average charges of £45 each time.
It has called on the Financial Conduct Authority (FCA) to take "strong action" to cap the charges and reduce the role of overdrafts in persistent problem debt.
A survey by StepChange of 1,019 clients found that those with overdrafts had been overdrawn in 11 of the last 12 months.
More than half of those advised by the charity in the first half of this year had overdrafts, amounting to 93,000 people owing an average of £1,679 on their overdrafts in addition to other debts.
StepChange said around 15,500 people made contact every month with overdraft debt, and it estimated that approximately 9,600 go into an unarranged overdraft in an average of five months in the year before they seek advice.
Around 6,000 would pay an average of £45 per charge, at a total of £225 for the year.
In 2014 the Competition and Markets Authority (CMA) found that more than half of overdraft users went into an unarranged overdraft and 10% did so for nine months or more.
StepChange chief executive Mike O'Connor said: "Overdrafts are the second most common type of debt we see and many of our clients, who are already in real financial difficulty, have been hit with penalty charges averaging £225 per year.
"It is time for the FCA to intervene, as they did with payday loans, to set a cap on the amount banks can charge for unarranged overdrafts. The FCA also needs to urgently look at how to reduce the role of overdrafts in problem debt so people can finally break free from this vicious cycle that far too many of them become trapped in.
"Without strong and swift action, hundreds of thousands of financially vulnerable people will see their problems get worse and millions of pounds will keep being added to the country's personal debt problem."
MP and Treasury Select Committee member Rachel Reeves said: "The proposals in this summer's report from the CMA did not go far enough. We need a proper effective cap on overdraft charges to help those most in need. That's why I am calling on the FCA to take action and I am urging them to set a cap for banks on unauthorised overdrafts as has been done for payday lenders.
"A recent study from Which? showed that the cost of borrowing £100 from some banks for 28 days amounted to as much as £90 in charges, compared with the maximum £22.40 on a payday loan. The FCA must look at this lending in exactly the same way and not shy away from setting a cap for banks too."
Which? director of campaigns and communications, Vickie Sheriff, said: "This is yet more evidence that many people struggle with unfair unarranged overdraft charges.
"The CMA's proposed maximum monthly charge cap will not be effective in curbing these exorbitant charges or protecting the most vulnerable customers. It's time for the FCA to step in and crack down on punitive fees."