Ofgem is investigating gas and electricity supplier E for potentially misleading its customers.
The regulator said today that the investigation was triggered by concerns over the supplier's approach to attracting new customers.
Companies are required to provide complete and accurate information to customers who are switching to a new tariff or energy supplier.
The BBC reported that the company, which has 100,000 pre-payment meter customers, could be fined up to 10 per cent of its turnover.
"The investigation will examine whether E breached licence conditions which require suppliers to provide information which is complete and accurate and is easily understood by customers when undertaking marketing and sales activities," the regulator said in a statement.
E said it had no comment to make.