LOS ANGELES — Climbing El Capitan and the famous big walls of Yosemite National Park got a bit harder last week.

The park added red tape to cut through before climbers can begin the physically grueling and mentally demanding feat of inching up vertical granite walls that take days to conquer and require spending the night suspended on tiny platforms hundreds or thousands of feet above Yosemite Valley.

Climbers will need to secure free permits before they can attempt multiday climbs on El Cap, Half Dome, the Leaning Tower and other big climbs beginning May 21.

The long-rumored plan will inevitably cause grumbling in the birthplace of American climbing and among a culture that embraces freedom. But it could help limit the number of climbers on classic routes that have become more crowded as the sport has grown exponentially in popularity.

“I think we’re going to have a lot of climbers whining and complaining because they were gifted this thing that they think is a right and it was really a privilege,” said Hans Florine, who with 170 ascents, has climbed El Cap more than anyone. “We were given incredible rag-tag Wild West privileges for the last 40 years in Yosemite. All they’re asking is to let us know you’re there.”

The two-year pilot program will put climbers on par with backpackers who have been required to get wilderness permits for decades to spend the night in protected backcountry areas of national parks and forests. Unlike hikers, though, the climbing permits will not at first be rationed on a quota basis that limits how many people can be on a designated route each day.

Jeff Webb, the wilderness manager for Yosemite, said the program will measure for the first time how many people are doing overnight or multiday climbs to see what areas are getting the most use and could eventually lead to limits on certain routes, such as The Nose on El Capitan.

The park will seek voluntary compliance but could fine climbers who break the rules, Webb said.

Yosemite is not the first park to require permits for multiday climbs. Zion National Park in Utah and the Black Canyon of the Gunnison and Rocky Mountain National Parks in Colorado also have permit systems.

Daniel Duane, a climber and author of “El Capitan: Historic Feats and Radical Routes,” said there was a certain sadness to the development because it was a reminder of an era when Yosemite’s signature climbs weren’t crowded.

Some climbers used to camp for months in the park and climb every day. City dwellers could call a friend on Thursday to plan a last-minute trip, drive all night from San Francisco or Los Angeles and hit the rock on Friday morning.

But the rise of climbing gyms has created a generation of new climbers that has the sport being included in the summer Olympics this year for the first time.