Billionaire businessmen Charles and David Koch are funneling money toward a special-interest group trying to defeat an effort to ban uranium mining around the Grand Canyon, the Phoenix New Times reported this week.

The uranium mining ban, which would grant federal protection to 1.7 million acres of land in the Grand Canyon, is backed by by environmental groups and native tribes. A temporary federal ban on new uranium mining at the Grand Canyon is already in place, but proponents want to make the ban permanent. U.S. Rep. Raúl Grijalva of Arizona and other Democrats have urged the Obama administration to create the buffer zone around the national park before President Barack Obama leaves office next year.

"I think future uranium mining poses the biggest threat to the Colorado River, the Grand Canyon and the native nations around it. No question about it, you need to create a significant protection buffer around it and guarantee it in perpetuity," Grijalva said earlier this month.

But some Republicans leaders have said the ban would be bad for the economy and have maneuvered in recent months to end the campaign. Republican critics of the ban include Gov. Doug Ducey, U.S. Sens. John McCain and Jeff Flake, and U.S. Reps.  David Schweikert, Trent Franks and Matt Salmon. Arizona Republican U.S Rep. Paul Gosar, who has received money from the Koch brothers, has called the ban a conspiracy put forth by “radical environmentalists” to “lock up 1.7 million acres of land” and kill local business.

Tax documents suggest the Koch brothers are helping to fund the effort. The Prosper Foundation — based in Arizona — has become one of the leading critics of the uranium mining ban. The group got $1.5 million, or some 80 percent of its budget, from a group called American Encore, which is led by Sean Noble, a political consultant connected to the billionaire Koch brothers. A report from the Prosper Foundation calls the conservation plan a “monumental mistake."

Polls show 80 percent of Arizona residents support the ban and nearly half of the population wants to see the government do more to protect the Grand Canyon.

“We know that these anti-public land efforts have a lot of money behind them,” Greg Zimmerman from the Center for Western Priorities, a conservation organization, told the Phoenix New Times. “It’s not surprising to learn that the Koch brothers and other wealthy, ultraconservative industrialists are funding these efforts to roll back conservation measures across the American West.”