Japan has set power-saving targets during the peak summer season to avoid a wider collapse of power grids.
Major power users have been asked to cut consumption by 25%, said the trade minister according to the Reuters news agency.
Small industrial users are being asked to use 20% less power and households 15-20% less.
Power capacity is down after power plants were knocked out because of the earthquake and tsunami.
The trade minister, Banri Kaida, told Reuters that the targets could cut demand by an estimated 15m kilowatts for the areas serviced by two utilities Tokyo Electric Power (Tepco) and Tohoku Electric Power.
He added that this means the utilities would not, in principle, have to impose rolling blackouts.
Tepco has been enforcing power cuts over the last month because of the damage to its nuclear reactors at the Fukushima power plant in north-eastern Japan.
Meanwhile, the Tokyo Stock Exchange has said it will delay a planned extension of its trading hours so that it can reduce power consumption.
The bourse said it will push back the plan, which was due to take effect 9 May, till the autumn.