The annual Cool Biz campaign started Wednesday, encouraging office workers to leave their ties and jackets at home to promote energy conservation and combat global warming by reducing the use of air conditioning.
It is the third year that the government has started the campaign a month early to enhance power saving amid the suspension of most of the nation's reactors following the 2011 Fukushima nuclear crisis.
Under the campaign, which was introduced in 2005, offices are encouraged to set air conditioners at 28 degrees and let their employees dress casually.
"We want people to pitch in by keeping their air conditioning at an appropriate temperature, while guarding against heatstroke by staying hydrated," Environment Minister Nobuteru Ishihara said.
Cool Biz will be in effect until the end of October. On June 1, the campaign will be stepped up to Super Cool Biz, which will allow workers to wear Hawaiian aloha shirts and polo shirts to the office.