Consumers' champion Which? has joined the Federation of Small Businesses (FSB) in a new call to examine the "broken" energy market in the UK.
In a joint letter to the Office of Fair Trading, energy watchdog Ofgem, and the recently-established Competition and Markets Authority, the groups say small businesses are finding rising energy costs a "major concern".
The move will be seen as a further blow by the 'big six' energy suppliers, as they wait to hear whether they are to come under scrutiny in a full inquiry into their competitive practices.
Which? executive director Richard Lloyd said individual and business consumers were being forced to struggle to pay their bills because energy companies were passing rises in wholesale energy prices straight through to their customers.
"We're saying to regulators you haven't addressed the uncompetitive nature of the wholesale market," Mr Lloyd added.
In their joint letter, Which? and the FSB said: "We want to see the presence of strong competition right across the industry drive affordable pricing that gives everyone the confidence they are paying a fair price for their energy."