Payday loan firm Wonga has been criticised by the Office of Fair Trading (OFT) for using aggressive and misleading debt collection methods.
The OFT said it had contacted the company to ensure its practices were "acceptable" after customers complained.
It said Wonga staff had tried to collect debts by scaring customers into thinking they had committed fraud and could be reported to the police.
Wording in call scripts used by staff stated that customers with jobs in the public or financial sectors should not find themselves in debt, and that this was stated in their terms of employment.
Wonga said it would appeal against the OFT as the inducements had been isolated and took place a long time ago, the BBC reports.
The OFT has imposed a requirement on Wonga that its communications must not, without appropriate justification:
• allege that a customer has, or may have, engaged in criminal conduct or refer to the consequences of such conduct
• state that a customer should not be in debt if the customer has a certain employment status or for any other reason.
The letters and emails were sent to customers who had claimed money back from Wonga by asking their card providers to reverse a payment made to the company.
They were also sent to some customers who had entered into debt management plans.
David Fisher, OFT director of consumer credit, said: "We have acted to ensure that Wonga does not behave this way again. I would like to make it clear to businesses that they must not adopt aggressive or misleading practices with their customers."
The OFT launched an extensive review of the payday lending sector in February. It expects to announce its findings and strategy to raise standards across the sector later this year.
More than £167,000 raised
Beware ‘temporary’ vulnerability
Celtic WM and Active Wealth