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The Trump administration will argue that the high cost of meeting Obama-era fuel economy standards discourages motorists from trading in less-efficient vehicles, as it sets about weakening the rules, said people familiar with the discussions.

As the Trump administration begins to dismantle Barack Obama’s ambitious auto efficiency regulations, California is said to be poised to retaliate by doing something that automakers have feared: de-coupling the state’s rules with those set in Washington.

California and the Trump administration are on a collision course over auto-efficiency regulations that could lead the White House to deploy the nuclear option: revoking the state’s cherished power to set its own limits on air pollution.

The Trump administration’s chief environmental regulator signaled a coming showdown with California, warning the state won’t dictate the future of ambitious automobile fuel economy regulations enacted by the Obama administration.

In 2012, the Barack Obama administration imposed regulatory standards that require significant increases in the fuel economy of automobiles. Intent on reducing regulatory costs, the Donald Trump administration is rethinking those standards. But it’s encountering a major roadblock: California.

The California Air Resources Board on Feb. 8 unanimously approved plans to retain two Obama administration Phase 2 greenhouse gas emissions rule provisions for medium- and heavy-duty trucks that would regulate glider kits and trailer emissions.

Whatever federal authorities may or may not do to alter parts of the U.S. Phase 2 regulation of greenhouse gases from trucks, California will keep regulations in place that are at least as tough as the October 2016 final rule, and might even get more strict and encompass aspects of nitrogen oxide emissions.

Eight states, including California, and five environmental advocacy groups have asked a U.S. appellate court for permission to intervene in a civil case between the Truck Trailer Manufacturers Association and two federal agencies concerning the final Phase 2 greenhouse-gas rule — just one month after TTMA filed its petition for review.

The rate of compliance for heavy trucks with the California Air Resources Board’s truck and bus regulation has decreased to 70%-75% from 85% over the past two years, according to estimates in a new CARB enforcement report.