The unexpected departure of GM CEO Fritz Henderson signals the board's impatience with the pace of change – especially compared with Ford.
Groups opposed to the decision have until Thursday to appeal it.
By 2016, a new car will pollute less and get more than 35 miles per gallon, but its sticker price will be at least $600 higher.
The plan will establish nationwide benchmarks for carbon emissions and fuel efficiency.
It will also cut Pontiac, as well as more jobs. But if dealerships and bondholders don't agree to the changes, bankruptcy looms.
So far, Ford is avoiding bankruptcy or a government bailout. Consumer confidence will be most important in securing its financial situation.
The industry itself bears some, but not all, of the responsibility, as GM and Chrysler seek more US aid.
The president called for tougher fuel-efficiency standards Monday and may let states regulate vehicle emissions of greenhouse gases.
A sharp drop in demand is driving the industry to pursue a bailout.