West Coast attorneys general oppose expanding a pipeline that crosses Idaho, Washington state and Oregon and carries natural gas, including biogas from a dairy.

The attorneys general on Wednesday asked the Federal Energy Regulatory Commission to deny TC Energy a permit to upgrade stations to pump more natural gas through the 1,377-mile pipeline.

Increasing the supply of natural gas could worsen global warming, according to Washington Attorney General Bob Ferguson, Oregon Attorney General Ellen Rosenblum and California Attorney General Rob Bonta.

“This project undermines Washington state’s efforts to fight climate change,” Ferguson said in a statement.

TC Energy said in a statement the project will meet increased demand for natural gas. Cascade Natural Gas, Intermountain Gas Co. and Tourmaline Oil Corp. have contracted to use all of the pipeline’s additional capacity.

“This further demonstrates the need for secure energy to supplement renewables as we work toward a cleaner energy future,” according to TC Energy.

The Gas Transmission Northwest pipeline runs from Kingsgate, British Columbia, to Malin in southern Oregon, and serves markets in Idaho, Washington, Oregon and California.

In 2020, TC Energy announced the pipeline was taking biogas, or renewable natural gas, from Threemile Canyon Farms, a large dairy in Boardman.

Northwest Gas Association executive director Dan Kirschner said upgrades to transmission lines will make partnerships between gas distributors and dairies possible.

“If you take what the AGs are saying to its logical conclusion, we put the pipeline system out of commission,” he said.

“If you take away the means by which renewable natural gas is delivered, it’s not a resource anymore. It’s back to being a waste.”

TC Energy proposes work at pump stations in the Idaho Panhandle, southeast Washington and north-central Oregon to increase the pipeline’s capacity by 150 million cubic feet a day.

In an environmental review, Federal Energy Regulatory Commission staff said they had no way to measure the project’s impact on the climate.

They calculated that if all the additional natural gas were combusted it would increase U.S. greenhouse gas emissions by about 3 million tons a year or 0.06% over 2020 levels.

In response, the U.S. Environmental Protection Agency asked the commission to “avoid expressing” the project’s greenhouse gases as a percentage of national emissions.

“This approach diminishes the significance of the project-scale GHG emissions,” according to comments attached to a letter from EPA Region 10 chief of environmental review Rebecca Chu.

In its application, TC Energy said increasing the supply of natural gas could displace fuels such as heating oil and lower carbon emissions.

The attorneys general disputed the need for more natural gas supplies since Oregon, Washington and California have laws calling for prohibiting or phasing out natural gas.

The Energy Information Administration projects that petroleum and natural gas will remain the most-consumed sources of energy in the U.S. in 2050, still more than doubling the energy generated from wind and solar.

Cascade Natural Gas serves customers in Washington and Oregon. Intermountain Gas supplies natural gas in southern Idaho. The Idaho governor’s office has indicated support for increasing the pipeline’s capacity.

Tourmaline is Canada’s largest natural gas producer. According to the company, the additional pipeline capacity will help meet demand for energy in the U.S. when wind and solar power are not available.

The Biden administration canceled TC Energy’s Keystone XL pipeline, which would have moved Canadian oil to the Texas Gulf Coast.