The Financial Conduct Authority has revealed that the "credit card market was not working well for some consumers" and said it will launch another study into the industry.
The UK regulator, which already released a report into the credit card industry in April of this year, said that customers who are over borrowing and paying unexpectedly high interest rates are the worst affected.
"The credit card market is well-established and hugely important for UK consumers, who hold around 70% of all credit cards in Europe," said Christopher Woolard, director of policy, risk and research at the FCA.
"We want to understand in more depth what drives consumers to make the choices they do and how firms develop the services they offer. We want to make sure that the market works well for all consumers and that card-holders get a fair deal."
Around 30 million Britons have a credit card, which account for £56.9bn (€71m, $89m) of outstanding debt.
The FCA said that it will further investigate the how firms recover their costs, to assess whether particular groups of consumers are over-borrowing or under-repaying their credit card balances and the possible reasons for this.
The watchdog said it is seeking feedback on the scope of the market study by 5 January 2015.