Sen. Cory Gardner Cory Scott GardnerJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Gardner on court vacancy: Country needs to mourn Ginsburg 'before the politics begin' MORE (R-Colo.) is being targeted by a six-figure ad campaign seeking to pressure him into supporting legislation aiming to protect Alaska's Arctic National Wildlife Refuge.

Alaska Wilderness League Action is spending $150,000 on ads that will start running on Monday and highlight the vulnerable Republican's record on drilling.

"Tell Senator Gardner to stop betraying Colorado values and support legislation protecting the Arctic National Wildlife Refuge," concludes the 30-second spot.

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It will run in the Denver media market as well as the OTT video-on-demand platform and in digital advertising statewide.

“Let’s be clear, on the most important public lands vote of his Senate career, Senator Gardner chose to side with oil and gas interests instead of standing up for Colorado values,” Alaska Wilderness League Action's Colorado political chairman, Gareth Martins, said in a statement.

“By rolling back more than 60 years of bipartisan protections for this cherished landscape, Senator Gardner has sent a message that no protected national park or wildlife refuge in Colorado or around the country is safe,” Martins added.

The legislation that Alaska Wilderness League Action is pushing Gardner to support would designate about 1.55 million acres of land in the Arctic National Wildlife Refuge as a component of the National Wilderness Preservation System. It was introduced last year.

A provision in a 2017 tax bill opened the refuge to drilling following years of debate over the matter.

Gardner's spokesperson defended the senator's environmental record in a statement to The Hill.

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"While the far-left is advocating for pie-in-the-sky proposals that would destroy jobs, Senator Gardner has successfully passed bipartisan legislation over the past decade that achieves real results to protect the environment and deal with climate change," Jerrod Dobkin said. "From protecting Canyons of the Ancients National Monument in Colorado to permanently reauthorizing the Land and Water Conservation Fund, Senator Gardner has been a leader when it comes to protecting the environment, and this attack is nothing more than an attempt by a political group to mislead voters."

Gardner is up for reelection this year, and is viewed as one of the GOP's most vulnerable senators.

--This report was updated at 2:34 p.m.