President Trump's decision to revoke a waiver that allowed California to set its own, stricter standard for car emissions drastically impacts the ability of New England states to regulate greenhouse gases.

“The Trump Administration is revoking California’s Federal Waiver on emissions in order to produce far less expensive cars for the consumer, while at the same time making the cars substantially SAFER,” the president tweeted this morning. “This will lead to more production because of this pricing and safety advantage, and also due to the fact that older, highly polluting cars, will be replaced by new, extremely environmentally friendly cars.

"There will be very little difference in emissions between the California Standard and the new U.S. Standard, but the cars will be far safer and much less expensive. Many more cars will be produced under the new and uniform standard, meaning significantly more JOBS, JOBS, JOBS! Automakers should seize this opportunity because without this alternative to California, you will be out of business,” he added in the tweet thread.

Five of the six New England states follow California's emissions standards for vehicles. (Only New Hampshire follows the less-stringent national standard).

“The Trump Administration’s attack on the California waiver is an illegal assault on states’ rights, clean air and the climate that will cost drivers billions more at the pump," Massachusetts Attorney General Maura Healey said in a written statement to WGBH News. "At a moment of global urgency, this administration is asleep at the wheel. It’s time to take away the keys.”

A decision to revoke the waiver would likely result in a legal challenge from California, Massachusetts and other states impacted by the decision.

The formal announcement is expected to come Wednesday afternoon at an event at the Environmental Protection Agency headquarters in Washington. Conservative and free-market groups have been asked to attend the event.

California's authority to set its own, tougher emissions standards goes back to a waiver issued by Congress during passage of the Clean Air Act in 1970. The state has long pushed automakers to adopt more fuel-efficient passenger vehicles that emit less pollution.

"The clean car standards are the nation's most robust program for reducing greenhouse gases in the country," said Emily Green of the Conservation Law Foundation. "And the states should have the authority— in fact they do have the authority under the Clean Air Act — to protect their citizens from these emissions and from harmful impacts of climate chaos that these emissions cause."

The Associated Press contributed to this report.