REI fostered a progressive reputation. Then its workers began to unionize

A position at REI was the first and only retail job Claire Chang says she ever considered taking.

A shopping mecca for outdoor enthusiasts, the retailer had cultivated a progressive reputation: promoting sustainability, famously closing on Black Friday to encourage people to play outside, giving workers a paid four-week sabbatical after 15 years and running as a co-op co-owned by its shoppers.

"I mean, we all started working at REI because of its values," says Chang, a visual presentation specialist who has been at the flagship store in New York's...