At dozens of national parks and historical sites around the United States, getting away from it all to revel in the country’s wide open spaces has taken on a whole new meaning.

Leave your dollars and coins behind, too.

The National Park Service is continuing to convert dozens of its sites across the country to cashless payments only, drawing complaints and, now, a lawsuit.

Starting in June last year, visitors to Rocky Mountain National Park in Colorado were told that they could not use cash to enter the park or use its campgrounds. The negative reactions were swift, with visitors raising privacy concerns and expressing confusion about why the American dollar would not be welcome in the U.S. parks system. Some noted that not everyone has credit or debit cards.

“The National Parks belong to the citizens,” wrote one person, among dozens who complained about the decision on the site’s Facebook page. “If we want to use legal tender then we should.”

“So now R.M.N.P. is becoming like Walmart self-checkout,” another wrote under the park’s announcement, which later stopped accepting comments and directed people to official channels.

The park service has been rolling out the policy for several years. In 2019, the service announced that it would only accept credit cards, debit cards and special park passes at Pipe Spring National Monument in Arizona. Similar changes came to Little Bighorn Battlefield National Monument in Montana, then Death Valley National Park in California, and this month, Hovenweep National Monument in Colorado and Natural Bridges National Monument in Utah, will go cashless. (At many sites, annual passes can still be purchased with cash.)