The start came a day after the government imposed restrictions on electricity consumption by large-lot users in eastern and northeastern Japan.
Eight automakers, including Nissan Motor Co. and Honda Motor Co., operated factories, while firms such as NTT DoCoMo Inc. opened some of their offices.
Employees arrived at Honda's factory in Sayama, Saitama Prefecture, by 6:30 a.m. to begin the day's work. A male employee said he came to work "as if today was Monday," adding that he didn't have any special feelings about working on the weekend.
Although the government's curb on power consumption applies only to large-lot users in the service areas of Tokyo Electric Power Co. and Tohoku Electric Power Co., some factories and companies in other regions will also operate weekends because the automobile industry's supply chain is spread across the country.
The industry has designated Thursdays and Fridays as substitute days off for working on weekends. DoCoMo offices that open Saturdays and Sundays will be closed Mondays and Tuesdays.