Moreover, the states contend these tougher standards are supposed to save both the planet and your bank account, cutting 1.8 billion metric tons of CO2 pollution and saving $1,650 per vehicle.
The lawsuit was virtually expected. Pruitt and the Trump administration have made their objections clear ever since taking office, and automakers have complained that the eco-friendly guidelines would raise costs and affect jobs. In particular, the Pruitt-era EPA has bristled over the Clean Air Act waiver that lets California set its own standards -- as 12 states follow California's lead, it can effectively thwart attempts to undermine existing guidelines. California finalized its own new standards in March 2017 knowing this would likely conflict with the EPA's plans, so it was really just a matter of time before the EPA tried a rollback and prompted a lawsuit.
There's no certainty that the lawsuit will succeed, but there's a real chance it will slow down the EPA's efforts. And that, in many ways, is the immediate goal. This could buy time for the participating states and would force car makers to develop their lineups on the assumption the tougher standards will remain intact for a while.