Montana GOP Senate candidate Tim Sheehy failed to disclose his role at the Property and Environment Research Center, a property rights and environmental research nonprofit that has a history of advocating for privatizing America’s federal lands and rolling back environmental laws including the Endangered Species Act.

Sheehy, a former Navy SEAL and wealthy businessman who is running against three-term incumbent Sen. Jon Tester (D-Mont.), joined PERC’s board in 2022, according to the organization’s filings with the IRS. But he failed to include his position at the think tank in his campaign financial disclosure, in violation of Senate rules, HuffPost has learned.

Public lands have emerged as a key issue in the race, with Tester painting Sheehy as a threat to their future and the Montana way of life. Sheehy’s failure to disclose his work at PERC could further complicate his already messy messaging on public lands policy.

Sheehy did report being a board director at other nonprofits; however, PERC does not appear on his disclosure form.

Sheehy’s campaign told HuffPost that Sheehy stepped down from the board prior to entering the Senate race last June. Asked why he didn’t disclose his role at PERC, campaign spokesperson Katie Martin said, “This omission was an oversight. We are working on amending the report.”

Senate rules require candidates to report both paid and unpaid positions held in the two years prior to their candidacy at any business enterprise, nonprofit organization, labor organization or educational institution.

PERC confirmed that Sheehy left its board before announcing his campaign last year. But as of Wednesday, PERC’s website still listed Sheehy as a board member.

“Tim was elected to the board in Fall 2022 due to his relevant background as a successful local entrepreneur in the area of forest health, wildfires, and ranching, all conservation issues we are engaged in,” Kat Dwyer, the organization’s marketing and media manager, said in an email.

Founded in 1980 and based in Bozeman, Montana, PERC describes itself as an “independent,” “nonpartisan” think tank that advocates for “free market environmentalism” — the idea that private property rights and market incentives lead to better environmental and conservation outcomes than government regulation.

Sheehy founded Bridger Aerospace, a Bozeman, Montana-based aerial firefighting company that relies almost exclusively on federal contracts. As HuffPost previously reported, Bridger has continued to pitch itself as a leader in the fight against climate change, even as Sheehy has toed the GOP line on the campaign trail and railed against what he calls the “climate cult” and “radical environmentalists.”

The millionaire businessman also owns a sprawling 7,000-acre ranch in Martinsdale, Montana, where he co-founded a cattle company and once offered exclusive, pay-to-play hunting excursions.

PERC is widely viewed as a right-wing outfit. It has deep historical ties to the fossil fuel industry and Donors Trust, a conservative group Mother Jones once dubbed the “dark-money ATM of the right” that has funneled millions of dollars to climate change-denier groups. Kimberley Dennis, the co-founder and board chair of Donors Trust, is a current member of PERC’s board of directors.

PERC says it is “inaccurate” to characterize the group as right-wing.

“PERC is a non-partisan conservation organization dedicated to conserving land, water, and wildlife through innovative market and incentive-based solutions,” Dwyer said. “PERC proudly works with policymakers across the political spectrum, including with the Biden administration on issues like forest restoration, wild horse adoption incentives, migration corridor conservation, and virtual fencing technology.”

Oil giant ExxonMobil and Koch family foundations have historically given PERC money, but PERC told HuffPost that it has not received funding from fossil fuel companies in the past 10 years.

Yet it remains a “partner” of the State Policy Network, a web of right-wing, industry-allied think tanks that for decades have waged war against environmental regulations, renewable energy and climate science. PERC supported the Trump administration’s industry-friendly rollback of Endangered Species Act protections and urged the Biden administration not to reverse the Trump-era changes.

“PERC has a well-established, 44-year history of advocating to gut and undermine our nation’s bedrock environmental laws in favor of private property rights,” said Matthew Koehler, media director at Wilderness Watch, an environmental organization based in Missoula, Montana. “Over the past five years or so, I’ve noticed them kind of going on a full court press to rebrand themselves and to soften some of their rhetoric, and through creative marketing make unsuspecting people think that their solutions — quote, unquote — are more palatable. But at the end of the day, this is an organization that is far-right.”

PERC simply can’t run away from its history, Koehler added.

Over its four decades, the group has advocated for privatizing federal lands, including national parks, increasing fees for visiting parks and other federal lands, and covering park maintenance backlogs by diverting funding from the Land and Water Conservation Fund, a decades-old program that uses offshore fossil fuel revenues to establish and protect parks, wildlife refuges, forests and wildlife habitat.

In a 1999 policy paper titled “How and Why to Privatize Federal Lands,” PERC’s then-director, Terry Anderson, and others laid out what they called “a blueprint for auctioning off all public lands over 20 to 40 years.”

PERC says its support for public land privatization is in the past. Anderson’s 1999 paper “is not representative of PERC’s current thinking,” Dwyer said.

“PERC firmly believes that public lands should stay in public hands. We do not advocate for nor support privatization or divestiture,” she said. “We support improved management of our public lands and using market-based incentives to achieve better management such as conservation leasing to allow conservation to be a use on public lands, addressing deferred maintenance, streamlining permitting for more forest restoration, and a more creative application of user fees in our national parks to support our superintendents and their parks’ unique needs.”

Much like PERC, Sheehy, a staunch supporter of former President Donald Trump, is trying to distance himself from a once full-throated embrace of pawning off federal lands. As HuffPost first reported, he advocated last year for federal lands to be “turned over” to states — a wildly unpopular position among voters in Western states, including Montana.

“Local control has to be returned,” Sheehy told the “Working Ranch Radio Show” in October, “whether that means, you know, some of these public lands get turned over to state agencies, or even counties, or whether those decisions are made by a local landlord instead of by, you know, federal fiat a few thousand miles away.”

Despite those comments, which came several months into his campaign, Sheehy says he opposes the sale and transfer of federal lands and has accused Tester and his allies of lying about his position.

“Tim believes public lands must stay in public hands,” Sheehy’s spokesperson said in a statement. “Tim believes Montanans know best how to manage our land, not the Washington bureaucrats.”

Sheehy and PERC apparently now agree on the issue of keeping public lands public, but they’ve been at odds when it comes to other policies.

PERC has long supported the idea of leasing federal lands for conservation and applauded the Biden administration’s recent rule to begin issuing such leases to put conservation and ecosystem restoration on equal footing with drilling, mining and other traditional land uses.

But like most Republicans in Congress, Sheehy has condemned the Biden administration’s changes to public land leasing.

“Instead of supporting the producers that they’re supposed to be enabling, they are putting constrictions in place that could potentially put them out of business,” he told “Working Ranch Radio” last year, referring to federal land managers. “So taking some of these leases out of agricultural production and moving them into conservation is deeply concerning.”

Nico Delgado, a spokesperson for Democratic super PAC American Bridge 21st Century, told HuffPost that Sheehy’s failure to disclose his role at PERC is part of a trend of “bending the truth with Montanans.” Among other things, Delgado noted, Sheehy admitted to lying to a national park ranger about how he received a gunshot wound, as the Washington Post first reported.

“Now he’s hiding being part of a group that wanted to jack up fees at national parks,” Delgado said.