SAN ANTONIO—Toyota Motor Corp. has scaled back production at its assembly plant here as a heat wave strains power supplies in the state.

Toyota may stop production on most days before 2 p.m. and shorten night shifts, effective immediately through mid-August.

The plant had already scheduled five days of summer shutdown next week, and added two additional days due to a global semiconductor shortage. The seven days of closures are unrelated to the heat wave.

Texas’ power grid operator took emergency measures July 13 to avoid rolling blackouts as electricity demand soared. The Electric Reliability Council of Texas is urging residents to cut power use during the hottest hours of the day and warned of a risk for rolling blackouts. Residents were asked to turn up thermostats, defer the use of high-power appliances, and turn off swimming pool pumps.

Toyota joins a slew of other companies in Texas, including Samsung Electronics Co. Ltd., that are using less power as the state copes a week of extreme heat.

“We are carefully monitoring the weather conditions and communicating with local authorities, and will adjust our plans accordingly,” Samsung said in a statement July 14.