The National Park Service on Tuesday extended by 30 days the comment period on a controversial proposal to significantly increase fees at the most popular national parks, including Glacier and Yellowstone.

Montana Sen. Steve Daines made the announcement, citing a request he and two other Western senators made in a letter last week to Mike Reynolds, acting director of the Park Service.

“It is critical that Montanans and Americans can afford to enjoy Montana’s national treasures,” Daines said. “A fee increase of this magnitude needs enough time for Montanans and our visitors to have their voices heard.”

To provide a comment to the Park Service on the proposed fee increase, click here. Deadline for comments is now Dec. 22.

Daines asked for an extended comment period along with Sens. Lisa Murkowski of Alaska and Cory Gardner of Colorado, saying that raising fees to the extent proposed would limit those who can afford to visit the nation’s popular natural attractions.

In late October, the Park Service said it would consider raising the entrance fees during peak season for 17 national parks, including those in Montana.

Under the agency’s proposal, the price per vehicle would jump from $30 to $70 while the price per individual would double from $15 to $30. Passes specific to each park would also increase.

“Although we respect the National Park Service’s attempt to find solutions for the deferred maintenance backlog, raising entrance fees to this degree could unfairly burden the public and create new barriers to the visitors that you hope to reach and inspire,” the letter read.

Interior Secretary Ryan Zinke said the fee increase would generate needed revenue for improvements to the parks’ aging infrastructure. The needs include roads, bridges, campgrounds and other services.

Zinke said the Park Service expects to raise $70 million a year with the proposal. The Park Service estimates that deferred maintenance across its parks stands at $11.3 billion, down from $11.9 billion in 2015.