Energy industry regulator Ofgem is to examine a claim that charity Age UK has been promoting unfavourable gas and electricity deals in return for cash.
The Sun newspaper claims energy deals offered by Age UK with supplier E.On may have been much more expensive than the cheapest offers from the firm.
In return, the Sun alleged, the charity had received about £6m from E.On.
Age UK has rejected the allegations, while E.On said its tariffs were competitively priced.
The Sun claimed that Age UK recommended a special rate from E.On which would typically cost pensioners £1,049 for the year - £245 more than its cheapest rate in 2015.
It also alleged Age UK received about £41 from energy supplier E.On for every person signed up, amounting to £6m a year.
BBC personal finance correspondent Simon Gompertz said it was standard practice for price comparison websites to receive a commission for passing on business.
Age UK would not comment on any payments it had received from E.On. But it said E.On "have been generous supporters of our charity over and above the number of customers on the tariff
http://www.bbc.co.uk/news/business-35488204