The government is investigating if any speculative actions are accelerating the record-breaking surge in wholesale power prices, along with a winter supply crunch.

Spot power prices hit a historic high for the fourth straight day on Tuesday. The Electricity and Gas Market Surveillance Commission is investigating whether inappropriate actions are driving up rates, according to a spokeswoman.

Prices began to rally last month as colder-than-normal winter weather boosted demand for heating. To make matters worse, utilities were forced to curb generation at gas-fired power plants due in part to lower-than-normal inventories of the fuel.

Japan’s power surveillance commission, which sits under the Economy, Trade and Industry Ministry, is also investigating if any electricity producers are purposefully withholding capacity from the market, the spokeswoman said. The commission hasn’t yet discovered any evidence of wrongdoing, she said.

The 24-hour average spot electricity price for next-day delivery jumped 27% to ¥79.4 per kilowatt-hour on Tuesday, according to the Japan Electric Power Exchange. That is the highest level since trading started in 2005, and well above the previous year’s average of ¥6.5.

Japan’s top electricity supplier has been unable to meet increased demand from its customers over the last few days. To avert a supply shortage, Japan’s grid manager ordered rival utilities to send power to the grid-operating subsidiary of Tokyo Electric Power Company Holdings Inc. on Sunday and Monday.

Sky-high power prices are likely to negatively impact the nation’s smaller electricity retailers, which have little generation capacity and are most reliant on the spot market. Most households and businesses won’t be affected by the volatility, as nearly all power supply contracts are linked to rates independent from the spot market.