A large coalition of environmental activist organizations are calling on the Biden administration to use a little-known regulatory maneuver to block a major natural gas expansion project in the Pacific Northwest.

In a letter to Environmental Protection Agency (EPA) Administrator Michael Regan, more than 140 groups, including the Center for Biological Diversity, Columbia Riverkeeper and Friends of the Earth, called on the agency to intervene in the approval process of the Gas Transmission Northwest XPress Project (GTNXP). They argued the action was necessary because the project would hurt decarbonization goals and lead to pollution.

"As fossil fuel combustion is the primary contributor to the greenhouse gasses causing climate change, phasing out fossil fuel combustion as rapidly as possible is a policy imperative agreed upon by an overwhelming consensus of climate scientists," the organizations wrote to Regan in their letter obtained by Fox News Digital. 

"We are in the midst of a crucial handful of years in which — by concerted action to reduce greenhouse gas emissions — we can still avoid locking in the worst impacts of climate change," they continued. "The President himself has called climate change an 'existential threat.'"

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Joe Biden, Michael Regan

President Biden talks to Environmental Protection Agency Administrator Michael Regan at a White House environmental justice ceremony last year. (Drew Angerer/Getty Images)

According to energy developer TC Energy, the $75 million project would leverage the firm's existing infrastructure to increase the operational GTN pipeline's incremental mainline capacity by 150,000 dekatherms per day, enough to power roughly 500,000 additional homes in the region. The GTN pipeline travels through Idaho, Washington and Oregon and serves California customers.

The expansion project — which would upgrade three particular existing compressor stations on the existing system that has transported natural gas for decades — received approval from the Federal Energy Regulatory Commission (FERC) in October after months of delays amid concerns over its climate impact.

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In their letter to Regan, though, the eco groups said the EPA could invoke its authority under the Clean Air Act to determine FERC's environmental review of the project was "unsatisfactory from the standpoint of public health, welfare or environmental quality," and refer it to the White House Council on Environmental Quality (CEQ). 

The groups referenced one previous example of the EPA invoking the authority when, in 1996, it intervened FERC rulemaking. They further noted that EPA’s authority is not time-barred or limited by the post-decisional stage of the process.

Federal Energy Regulatory Commission commissioner Willie Phillips waits to testify during the Senate Energy and Natural Resources Committee hearing on Thursday, March 3, 2022, to review FERC's recent guidance on natural gas pipelines." (Bill Clark/CQ-Roll Call, Inc via Getty Images)

Federal Energy Regulatory Commission Chairman Willie Phillips waits to testify during a Senate Energy and Natural Resources Committee hearing in March 2022. (Bill Clark/CQ-Roll Call, Inc via Getty Images)

"We urge EPA to refer this decision to CEQ on several counts: the project’s enormous social costs to society; its resultant emissions making existing state-level climate commitments impossible to meet; FERC’s stark failure to meet its statutory obligations under [National Environmental Policy Act (NEPA)], which includes its refusal to consider several of EPA’s recommendations as a cooperating agency; and for its inconsistency with CEQ NEPA guidance," they continued.

And they pointed to EPA's own comments from 2022 on GTNXP, identifying its "environmental concern."

However, the groups' effort was blasted by TC Energy, which noted that extreme cold conditions are sweeping across the country and that Americans largely rely on natural gas for heat. According to Fox Weather, a recent arctic blast led to freezing temperatures, at least 10 deaths and transportation delays nationwide, and a second blast is expected to impact 75% of Americans this weekend.

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"With cold temperatures gripping the nation, it is imperative that consumers across the United States have access to affordable and reliable supplies of natural gas," TC Energy spokesperson Michael Tadeo told Fox News Digital. "Since 2014, demand on the existing GTN system has surged more than 50 percent. The GTNXP project, consisting of limited software and other upgrades to existing infrastructure, would help meet this increasing demand and help lower natural gas prices for consumers."

"FERC’s bipartisan approval of this project reaffirmed that it is in the public interest and is critical to keeping energy affordable and reliable in California and the Pacific Northwest," Tadeo said. "With strong support from labor unions, consumers and elected officials, TC Energy remains committed to putting this important project into service as soon as possible."

Rep. Lori Chavez-DeRemer, R-Ore., was one of several lawmakers to call on FERC to approve the natural gas pipeline project. She argued it would support "domestic energy production and boost our energy security while also helping lower utility bills for families." (Al Drago/Bloomberg via Getty Images)

Nearly half of U.S. homes rely on natural gas, piped directly to a furnace, for space heating. Another 40% rely on electricity — the majority of which is generated by natural gas nationwide — to power electric space heaters, according to a Washington Post analysis of the 2017-2021 American Community Survey.

Still, environmentalists have repeatedly pushed initiatives to both decrease natural gas hookups in new construction and replace natural gas-fired power plants with green energy sources.

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"I'm at a loss as to how we're supposed to deliver the energy that consumers need when they need it most if we don't have the capacity to deliver that energy, if we're not allowed to upgrade facilities and accommodate the energy that growth is already demanding," Northwest Gas Association Executive Director Dan Kirschner told Fox News Digital. "It's not a matter of the future. This is demand that's online."

"These activists and others are focusing all their firepower on even the smallest projects," Kirschner said. "This is not an expansion in the true sense of the word — there's no piping laid in the ground. It's an upgrade. It's upgrading facilities and software to push a little more gas across through the system, to serve needs that we know are there, especially for these coldest days of the year."

In addition to the Northwest Gas Association, GTNXP has received support from local labor unions and Republican lawmakers.