“It’s definitely taking advantage of people who love their jobs and don’t want the park to suffer,” said one of the employees, who said they volunteered for three weeks before being hired.

NPR spoke with four seasonal and two full-time workers employed by the National Park Service who described the situation. NPR has agreed not to publish the names of the employees because they are not permitted to speak publicly and feared retribution.

Yosemite depends on seasonal workers to perform a variety of jobs from May through October, when the park receives most of the more than 4 million visitors who typically enter the grounds. The national park, located near Mariposa, Calif., is one of the most visited in America.