Shares of Tokyo Electric Power Company fell on the Tokyo Stock Exchange on fears that it may be nationalised.
It was the most actively traded stock on the bourse on Wednesday, falling 12% to 186 yen.
On Tuesday, TEPCO asked the government for an extra 690 billion yen ($US9 billion) to help pay compensation claims.
Energy Minister Yukio Edano has asked it to consider temporary state control to ease its financial burden.
The company has already received $US7.1 billion in government funding, but faces claims and costs of almost $US100 billion due to radiation leaks at the Fukushima Daiichi nuclear plant.
The plant was damaged by the earthquake and tsunami on 11 March. Some 80,000 people had to be evacuated from the surrounding area.
The BBC reports the twin disasters have since forced the closure of 15 of TEPCO's 17 nuclear plants.
Last week, TEPCO announced that it was raising electricity prices for corporate clients for the first time in more than 30 years.
Mr Edano said the company needs a huge cash injection to ease its problems.
TEPCO is expected to submit a detailed business plan to the government by March next year, indicating how it plans to restructure its operations amid all the problems.
