Over the next few weeks, almost every bank is increasing its overdraft rate to 40% interest.
But fact they've all chosen "very similar prices" has seen city regulator, the Financial Conduct Authority (FCA), write to them demanding they explain themselves.
And that's good news for people who are currently overdrawn.
As Martin Lewis, founder of MoneySavingExpert.com, explained: "This subtle note is actually a slap on the wrist for the banks and is exactly what I and others have been calling for behind the scenes."
That's because, as well as asking them about how they reached the 40% number, the FCA has told them they have to treat people who could lose out as a result fairly.
The new rates come after rules were announced preventing providers from charging higher prices for unarranged overdrafts than for arranged overdrafts.
Firms will need to charge a simple annual interest rate - without additional fees and charges for using an overdraft.
The changes will mean the new rates for some customers will be around double what they have been previously.
Some critics of the plans have argued they could penalise people who borrow responsibly and remain within their arranged overdraft limits.
"The fact the regulator is saying this in writing, in black and white, is important," Martin said.
"It means customers should make a formal complaint to their bank if the overdraft changes are over-expensive, unaffordable and detrimental to their financial health.
"Then even if the bank rejects their complaint, individuals have a right to go on to the free financial ombudsman.
"As the ombudsman doesn’t just look at the law but also looks at standard industry practice – the fact the regulator has said this effectively defines this standard industry practice, meaning consumers can expect cases to be looked at favourably."
What the FCA said to the banks
The FCA was clear that banks had to make sure anyone losing out as a result of the new rates was looked after.
"We expect firms to take positive steps to help customers who may be worse off or in financial difficulties as a result of these changes," the FCA said.
"We have asked to see their plans for how they are dealing with the most affected customers."
And it was more than just information the regulator was asking for.
"We expect banks to take steps to support [affected customers], for example firms could reduce or waive interest, offer a continuation of overdraft borrowing at current rate of interest, or agree a repayment programme – including a personal loan," he added.
The FCA told worried customers to contact their provider, and had a final warning for banks.
"We will be keeping a close eye on the market and we will act should we see continued harm," the regulator said.
