A group of 20 senators and representatives has formed a de facto “anti-parks caucus” in Congress and is waging the most significant legislative and ideological challenge to America’s national parks in decades, says a new report released Monday by the Center for American Progress. The analysis finds that this anti-parks caucus is composed of less than five percent of Congress but is responsible for introducing dozens of bills to block the creation of new national parks, end America’s most effective parks program, and sell off public lands.

Eight anti-parks caucus members also participate in the Federal Land Action Group, a group formed last year with the sole purpose of developing land grab legislation that would transfer federal land to state and local control.

“Public land grab efforts almost never rise up from local communities,” according to Jim Caswell, BLM director under President George W. Bush. “They are instead galvanized by partisan politics, mainly at the national level, where the real agenda is wresting public lands from public hands and ultimately privatizing them for nonpublic uses.”

Such partisan politics ring true with the 20-member anti-parks caucus which includes Reps. Rob Bishop (R-UT) and Jason Chaffetz (R-UT), and Sens. Lisa Murkowski (R-AK) and Ted Cruz (R-TX).

The CAP analysis indicates that the far right flank of the Republican party has been a driving force behind the emergence of the caucus. While Tea Party affiliation only comprises 12 percent of Congress as a whole, it makes up 45 percent of the anti-parks caucus. Furthermore, every member of the anti-parks caucus can be described in at least one of the following ways: is member of the Tea Party; was challenged by a Tea Party candidate in a recent primary; or represents a district that is less competitive than average.

Members of the caucus have made statements supporting the underlying values fueling extremist attacks on public lands. In 2014, for instance, Sen. Cruz said, “We should be reducing the amount of federal land that the BLM controls and the amount of land that the federal government owns.” Nine of the 20 anti-parks caucus members have introduced legislation to undermine the Antiquities Act of 1906, a law eight Republican presidents and eight Democratic presidents have used to designate national monuments. Other attempts to roll back protections on lands set aside for all to enjoy flies in the face of traditionally bipartisan conservation efforts dating back to 1872 when Congress created Yellowstone National Park.

Meanwhile, the National Park Service is poised to kick off National Park Week (April 16 to 24) as part of this year’s celebration of the 100th anniversary of the agency’s creation. Three out every four registered voters believe that the United States benefits from the National Park system a “fair amount” or a “great deal,” according to polling conducted by Hart Research Associates in January 2016. Furthermore, 83 percent of Americans say they would have a “favorable” reaction to their representative in Congress taking “a strong stand in support of policies to protect and strengthen national parks.”

“In this Centennial year for the national parks, Americans are rightly mystified by why Congress is trying to dismantle the nation’s proud bipartisan conservation tradition by selling off public lands and stopping the creation of new parks,” said Jenny Rowland, research and advocacy associate at the Center for American Progress and author of the report. “The recent rise in congressional attacks on national parks can be traced to the emergence of this small Anti-Parks Caucus and — thankfully — does not reflect the values of most Americans or even most Members of Congress.”

Mary Ellen Kustin is the director of policy for the Public Lands Project at the Center for American Progress.