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Association Challenges California's Clean Truck Partnership

The Western States Trucking Association is challenging a deal that truck and engine makers made with California to continue to meet the state's truck emissions rules even if it lost the federal authority to implement those rules

Deborah Lockridge
Deborah LockridgeEditor and Associate Publisher
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June 27, 2025
Association Challenges California's Clean Truck Partnership

California's NOx and zero-emission truck regulations are dead..... but are they really? 

Image: HDT Graphic

3 min to read


The Western States Trucking Association is challenging a deal that truck and engine makers made with California to continue to meet the state's truck emissions rules even if it lost the federal authority to implement those rules. 

The association filed a petition with California’s Office of Administrative Law, alleging that the California Air Resources Board, by entering into the Clean Truck Partnership, improperly adopted what was in reality a regulation in violation of the California Administrative Procedure Act.

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CARB, the Truck and Engine Manufacturers Association, and truck and engine makers entered the Clean Truck Partnership in the summer of 2023.

In that deal, the OEMs agreed to comply with CARB’s Advanced Clean Trucks and Heavy-Duty Omnibus regulations, “irrespective of the outcome of any litigation challenging the waivers or authorizations for those regulations or of CARB’s overall authority to implement those regulations.”

Truck makers did this in exchange for California's commitment to work collaboratively with manufacturers to provide lead time to meet specific regulatory requirements before imposing new ones.

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Congress vs. California Air Resources Board

After Congress recently voted to revoke the Environmental Protection Agency waiver for California’s Advanced Clean Trucks regulation and the Heavy-Duty Low-NOx Omnibus rule, CARB has taken actions indicating it’s forging ahead in its truck emissions goals by expecting truck and engine makers to abide by the Clean Truck Partnership agreement.

On May 23, CARB issued a Manufacturers Advisory Correspondence document saying it will continue to certify engines and trucks pursuant to the ACT and Omnibus regulations for model year 2026 in part to “facilitate meeting the commitments of the [CTP]," according to the WSTA petition.

After President Trump signed the congressional orders revoking the EPA waivers, California Gov. Gavin Newsom issued an executive order that, among other things, continues the Clean Truck Partnership work and requires reports on progress every six months.

Western States Trucking Calls CTP 'Invalid Underground Regulation'

“The CTP creates new regulatory obligations for virtually an entire industry —  including the requirement to follow regulations that are not authorized by federal law,” said the association in its petition.

“It also purports to grant CARB new powers, such as the power to require new vehicle and engine certifications to meet requirements that do not have federal authorization. Although the CTP stands in for CARB regulations, CARB did not comply with the APA in introducing this alternative regulatory regime. Thus, the CTP is an invalid underground regulation.”

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The petition notes that if CARB had gone through the APA procedures, it would have had to publicly explain and justify the implementation of its stringent zero-emission vehicles policy in the face of federal preemption, and purchasers and fleet operators would have had the opportunity to comment on the issues the CTP will create.

Critics: Petition is ‘Attack on the Industry’

Critics of the Western States Trucking Association petition say the Clean Truck Partnership has helped provide certainty to businesses that have already adopted electric trucks, at a time when shifting federal regulations have caused uncertainty.

The WSTA petition undermines that certainty, critics say, calling the challenge an attack on the future of the trucking industry.

One of those critics is Craig Segall, who helped negotiate the Clean Truck Partnership Agreement as CARB deputy executive officer and assistant chief counsel. 

He said the association's attack on the agreement would set the trucking industry back and called on truck manufacturers to stand by the agreement they signed two years ago.

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“The companies shook hands with California on a workable path forward," Segall said in a news release. 

"Will they now stand behind their commitments as others attack them? Or will they stay silent during this attack? My hope is that they will stand up for the electric future they claim to support.”

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