Adrienne Skabelund

Union organizers say the effort began when the Trump administration sought to fire hundreds of probationary park employees last spring.

Organizer Michelle Vought says they also hope to address issues like pay and housing.

Staff at Glacier, Rocky Mountain, and Grand Teton National Parks are also filing to unionize.

It comes months after employees at Yosemite and Sequoia Kings National Parks moved forward with their own unions.

For NPR News, I'm Adrian Scabland in Flagstaff.