Ford has a lot riding on the new Bronco, returning after 25 years off the market.
GM had previously sided with the Trump administration in a legal fight over California setting its own emissions standards.
As the auto industry reopens, unions say they are concerned about working conditions in plants.
Amid fears that Beijing will control the world market in electric vehicle batteries, some Brits are backing an alternative: hydrogen.
The coronavirus pandemic forced Ford, GM and Fiat Chrysler to close factories and halt production. They're expected to report large losses.
Auto production made the biggest manufacturing gains in June, but an increase in COVID-19 cases now threatens that progress.
Among the steps General Motors says it will take: providing additional protective gear, and taking workers' temperatures when they arrive.
The plant is situated in a California COVID-19 hot spot.