A group of state attorneys general on Wednesday urged the National Park Service to scrap its proposal to more than double the entrance fee at 17 popular national parks.
The top government lawyers from 10 states and the District of Columbia sent a letter saying the increase could put access to the parks out of reach for many Americans.
"We cannot let the most popular and awe-inspiring national parks become places for the wealthy," they said in the letter to the Park Service's acting director.
All the signers are Democrats except for Arizona's Mark Brnovich, a Republican.
The AGs say the increase is inconsistent with the laws governing the park system because the administration did not provide an economic analysis to support its claims that raising fees would increase revenue.
The Park Service estimates that higher fees will generate an additional $70 million a year, more than half of which would be used to chip away at a backlog of maintenance and infrastructure projects. But the AGs say the increase actually could reduce the number of visitors and revenue.
It would particularly hit lower-income people who already use the parks less frequently than those with more money, they said.
In a separate statement, California Attorney General Xavier Becerra suggested he and his colleagues could take legal action if the Park Service moves ahead with the plan, which would boost the entrance fee to $70 per vehicle at the targeted parks, up from $25 or $30.
The fee would go into effect during peak season at heavily visited parks, including Glacier, Grand Canyon, Yellowstone, Yosemite and Zion in the West, and Acadia and Shenandoah in the East. Five of the AGs who signed the letter represent states that include parks that would be subject to the fee increases; six do not.
Raquel Coombs, a spokeswoman for Maryland Attorney General Brian Frosh, said it didn't matter that Maryland does not have a park that would be affected: "Everyone should have access to our nation's national parks," she said.
The letter was also signed by the attorneys general of Maine, Massachusetts, New Mexico, New York, Oregon, Rhode Island and Washington.
The AG's also question the rationale, saying Trump has proposed reducing the service's overall budget. The Park Service says the administration's budget calls for Congress to allocate more money for park maintenance backlogs.
It has received some 65,000 comments on its proposal and has extended the public comment period to Dec. 22.
Associated Press writer Felicia Fonseca in Flagstaff, Arizona, contributed to this report.