Japan's government is urging businesses and households to cut their electricity use by up to 15%.
Japan is facing power shortages because all its 50 nuclear reactors have been taken offline in the wake of the Fukushima nuclear disaster.
Public confidence in the nuclear industry has been shaken by the meltdowns at Fukushima, triggered by last year's massive earthquake and tsunami.
Calls for electricity reduction will take effect from July to September, the BBC reports.
This time around the move to save power is not mandatory, unlike cuts imposed in the eastern parts of the country last summer after the nuclear crisis.
It is in the heavily industrialised area of western Japan, served by Kansai Electric Power, that customers have been asked to cut electricity usage by 15%.
Chief Cabinet Secretary Osamu Fujimura, after a government meeting discussing power shortages, says that there is a "need to widely instigate power-saving measures" due to the shutdown of nuclear facilities.
"Save power this summer."
Japan's last nuclear reactor went offline for routine maintenance two weeks ago and none have been switched back on so far.
The government has been reluctant to order restarts of the nuclear plants against the public's wishes, though surveys show that almost all big businesses expect their earnings to be affected, with some preparing to move more manufacturing abroad.
Before the Fukushima meltdowns, nuclear energy powered up to 30% of the country's electricity.