Seeking to kick-start electric car sales outside of California, the lobbying group that represents a dozen automakers said Monday that it sent letters to nine state governors urging them to help spur zero-emissions vehicle demand.

In the letters, the automakers urge the state governors to boost investments in electric-car charging infrastructure, expand tax credits and other incentives, and buy more emissions-free vehicles for state government fleets. Stating that California is "leading by example," the letters disapprovingly say that each state is not living up to its promise to help grow zero-emissions cars such as electric and fuel-cell vehicles to 15 percent of local car sales by 2025.

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The Alliance of Automobile Manufacturers, which represents a dozen car manufacturers, said Monday that the letters were sent between May 31 and June 6 to the governors of Connecticut, Maine, Maryland, Massachusetts, New Jersey, New York, Oregon, Rhode Island, and Vermont. Those states follow California's zero-emissions vehicle mandate, which requires automakers to attain zero-emissions vehicle credits based on a complex accounting system.

The letters point out that zero-emission vehicle sales in the nine states last year were well off sales goals set for 2025. In the letters, the Alliance compares California's nearly 5 percent zero-emissions figure last year to each state's far lower share of zero-emissions vehicles. 

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In Oregon, for instance, about 2.2 percent of new cars sold in 2017 were zero-emissions vehicles. In Rhode Island, it was less than 1 percent. 

The zero-emissions mandate's future hinges on whether the EPA continues to allow California—and states that follow its rules—to mandate vehicle emissions more stringently than federal standards.

The Alliance represents some major producers of electric and zero-emissions vehicles, such as General Motors and Toyota, but its roster doesn't include some car manufacturers such as Nissan and Honda.