Boeing Co., Archer-Daniels-Midland Co., Delta Air Lines Inc. and other companies are urging Treasury Secretary Janet Yellen to back tax policy they say is needed to build a thriving US industry for green jet fuel. 

Their letter to Yellen Wednesday, signed by about 70 companies, is the latest salvo in a lobbying fight over how to monitor carbon dioxide emissions across the supply chain for sustainable aviation fuel, or SAF. 

Biofuel producers and airlines are pushing for SAF tax rules under President Joe Biden’s landmark climate law that would track emissions through an approach already used by the US Energy Department. Any new model would risk further delay, they warn, adding that a rival approach out of the United Nations — which is being encouraged by fuel retailers and environmentalists — is too outdated and lacks flexibility.

“Modeling uncertainty today is a multi-year development problem due to the buildout schedules of SAF production facilities,” the companies wrote. “We underscore the urgency for providing clarity on this issue as soon as possible.” 

Biofuel makers say without what their preferred model for measuring carbon from the SAF supply chain, the market will lack signals needed to slash aviation emissions and spur new technologies and jobs. Meanwhile, trade groups representing truck stops and fuel retailers argue that the UN-crafted approach is more stringent and would guard against raw materials like vegetable oils shifting to SAF production and away from green diesel used in heavy road vehicles.

The letter to Yellen — also signed by Deere & Co., crop trader Bunge Ltd. and top ethanol maker Poet LLC — is set to be widely released on Wednesday as Biden visits Minnesota to focus on rural investments, including a push to boost availability of domestic biofuels.