The Labour Party has vowed to cap energy prices if it gets into power.
Shadow Chancellor John McDonnell made the promise after npower announced a 9.8% price rise for many of its customers. The hike is expected to add roughly £109 to the cost of annual dual fuel bills.
The Big Six supplier said the rise, which comes in the face of rising wholesale costs, had been a difficult decision to make. Other providers are now expected to follow suit.
Regulator Ofgem disagreed with the move, saying it could not see the need for such significant price rises in a market where energy is bought far in advance.
In a BBC interview, Mr McDonnell said: “We would control them. We would legislate to control them. We can’t allow this to keep going on.
“You would introduce legislation in Parliament. You would limit the amount they can increase their prices by.”
Lawrence Slade, CEO of Energy UK, took a different view, suggesting the majority of the components which make up an average energy bill are outside of suppliers’ control and are adding pressure to the market.
He said: “The energy industry has only recently undergone an extensive two-year investigation by the Competition and Markets Authority. Their recommendations must be allowed to be introduced.
“The industry is already taking action and is committed to ensuring the market works for consumers and helping households manage their energy consumption and spend.”
Energy suppliers will be required to take part in trials this summer to help customers get the best deal.