A coalition of 17 states and the District of Columbia, led by California, is suing the Environmental Protection Agency over its plan to change vehicle efficiency standards. The states are asking a court to review the EPA's proposed actions, arguing that they violate the Clean Air Act."We're not looking to pick a fight with the Trump administration, but when the stakes are this high for our families' health and our economic prosperity, we have a responsibility to do what is necessary to defend them," California's attorney general, Xavier Becerra, said.In a news release, the states said their lawsuit "seeks to set aside and hold unlawful the EPA's effort to weaken the nation's existing clean car rules ... based on the fact that the EPA acted arbitrarily and capriciously, failed to follow its own regulations, and violated the Clean Air Act."Specifically, the EPA is reconsidering Obama-era rules designed to reduce greenhouse gas emissions from cars. The regulations call for average fuel efficiency to increase to 54.5 mpg by 2025. EPA head Scott Pruitt has said the current standards "may be too stringent," and has initiated the process of rewriting them.In its announcement last month, the EPA said that the ambitious Obama-era standards present "challenges to auto manufacturers" and impose extra costs on consumers.In response Consumers Union, the advocacy division of Consumer Reports, said that efficiency standards actually save consumers money.And a report released by the Institute for Policy Integrity at the New York University School of Law said the EPA's reasoning was "not grounded in fact." For instance, the EPA says lower gas prices are making fuel-efficient cars less attractive, and cites flagging demand for electric cars as a sign the goals are unrealistic. However, the report notes, "both fuel prices and electric vehicle sales are in fact rising."The legal battle between California and the EPA ultimatelycouldlead to two competing emissions standards — one for California and the states that follow it, and another for the rest of the country. That's an outcome automakers would prefer to avoid. Copyright 2018 NPR. To see more, visit http://www.npr.org/.