In a strongly-worded letter [PDF] to the CEOs of seven major auto manufacturers, California Air Resources Board chair Mary Nichols defended California’s efforts to curb greenhouse gas emissions from cars and trucks and accused the trade group, the Alliance of Automobile Manufacturers, of misrepresenting California’s cooperation with federal agencies in letters to Congress.

At issue, wrote Nichols, are letters the Alliance sent to Congressmen Darryl Issa (R-Vista) and Fred Upton (R-MI) in January, calling “our commitment to a national program into question.”

“For the Alliance to suggest we are no longer committed to a cooperative effort is disingenuous at best, and incorrect,” wrote the Air Board chairman.

Nichols called on the executives to “distance” their companies “from future efforts by the Alliance to undermine the achievement of our mutual goals to set standards that will provide American consumers with cleaner and more efficient vehicles.”

The letter comes just as California and federal agencies announced a shared deadline for their collaboration to set national fuel economy and greenhouse gas standards for model year 2017-2025 cars and trucks.

Margot Roosevelt of the Los Angeles Times has more, including a response from an Alliance vice president who reportedly would not address the Nichols letter directly, but did express support for the shared fuel standards deadline.