More than a million credit card users who are struggling financially have had their credit limits increased without asking, a charity has said.
Such borrowing could make their financial problems worse, so Citizens Advice is calling for a ban on unsolicited increases in credit card limits.
It wants Chancellor Philip Hammond to include such a move in the Budget.
But providers say protection is being improved.
Citizens Advice said its research, based on a sample of 1,300 people with credit cards, suggested as many as six million cardholders may have had their credit limits put up without their consent in the last year. Some 1.4 million of those would be struggling financially.
Providers have agreed to a voluntary code being developed by the Financial Conduct Authority (FCA), the City regulator, which would see restrictions and choice on credit limits.
They will start asking new customers for their consent before raising limits, and give them the option to carry on receiving uninvited increases. Existing customers will be given the option to ask their lender to require their consent.
But Citizens Advice is calling for the chancellor to impose a clear ban on increases which customers have not even requested.