The energy regulator is to investigate whether Ovo Energy gave some of its customers inaccurate information relating to how much gas and electricity they'd used.
Ofgem today launched its investigation into the firm over the information it gave to some customers about their usage last winter, and the figures it put in annual statements.
The investigation, launched following complaints from customers, will examine whether Ovo Energy breached the conditions of its licence to supply gas and electricity, about giving customers accurate information which is not misleading.
Incorrect figures can mean customers are given inaccurate bills and annual statements, and so could mean they are unable to manage their accounts properly and make an informed decision of whether to switch or stay.
What happens next?
Investigations like these can usually take around a year, but Ofgem can't give an exact timeframe.
An Ofgem spokesperson said: "The opening of this investigation does not imply that we have made any findings about non-compliance by Ovo Energy."
If Ovo Energy is found to have breached the licence conditions it could be forced to pay a fine and compensation to customers.
An Ovo Energy spokesperson said: "We have a great track record in customer service and are always open to ways to improve it."