As the White House grapples with how to rewrite vehicle emissions rules slashed under President Donald Trump, California’s two U.S. senators are urging President Joe Biden to set a firm date to phase-out gas-powered passenger vehicles.

In an unreported letter going to Biden Monday, Democratic Senators Alex Padilla and Dianne Feinstein called on Biden “to follow California’s lead and set a date by which all new cars and passenger trucks sold be zero-emission vehicles.” They also urged Biden to restore California’s authority to set clean car standards.

In September, California Governor Gavin Newsom signed an executive order directing the state’s air resources agency to require all new cars and passenger trucks sold in California to be zero-emission by 2035.

Biden’s campaign in 2020 declined to endorse a specific date to end gas-powered vehicle sales, but he has vowed to dramatically boost electric vehicles and charging stations.

In January, Biden said the administration would replace the federal government’s fleet of 650,000 vehicles “with clean electric vehicles made right here in America made by American workers.”

The senators also say Biden should use a compromise deal that California struck with automakers including Ford Motor Co, Honda Motor, BMW AG and Volkswagen AG that falls between the Trump administration and Obama-era requirements.

“We believe the national baseline should, at an absolute minimum, be built around the technical lead set by companies that voluntarily advanced their agreements with California,” Padilla, who replaced Vice President Kamala Harris in the Senate, and Feinstein wrote in the letter seen by Reuters. “California and other states need a strong federal partner.”

Shortly after taking office, Biden ordered U.S. agencies to revisit fuel efficiency standards by July.

The Trump administration in March 2020 finalized a rollback of fuel economy standards to require 1.5% annual increases in efficiency through 2026, well below the 5% yearly boosts in Obama-administration rules it discarded.

Then-President Donald Trump repeatedly targeted California, a Democratic bastion that tangled with Trump on multiple fronts during his tenure.

The Center for Biological Diversity estimates the California deal improves fuel economy 3.7% year-on-year between 2022-2026.

Biden also directed the Environmental Protection Agency and the National Highway Traffic Safety Administration by April to reconsider Trump’s 2019 decision to revoke California’s authority to set its own auto tailpipe emissions standards and require rising numbers of zero-emission vehicles.

A White House spokesperson declined to comment Sunday on the timing of any announcement on California’s vehicle authority.

California’s vehicle emissions standards are followed by 13 other states and the District of Columbia accounting for more than 40% of the U.S. population.

In January, General Motors said it aspires to end all gasoline passenger car and truck sales by 2035. Volvo, a unit of Zhejiang Geely Holding Group, said its entire car lineup will be fully electric by 2030 and Ford’s European lineup will also be fully electric by 2030.

The Alliance for Automotive Innovation, a trade group representing major automakers, declined to comment Sunday but last month backed nationwide rules to achieve vehicle emissions reductions roughly midway between the Trump and Obama standards.