WASHINGTON (AP) — Democratic senators are harshly criticizing a National Park Service plan to impose steep increases in entrance fees at 17 of its most popular parks, including the Grand Canyon, Yosemite, Yellowstone and Zion.

The senators say the plan would exclude many Americans from enjoying national parks and call the proposed fee levels "arbitrary and unjustifiable."

Under a plan announced this week, visitors to many national parks would be charged $70 per vehicle during the peak summer season, up from $25 or $30 per vehicle now. Officials say the higher fees are needed to address a backlog of maintenance and infrastructure projects.

Washington Sen. Maria Cantwell and other Democrats say the proposal is especially egregious because the Trump administration is recommending severe budget cuts for the park service.