Employees at an Alamo Drafthouse theater in Colorado have authorized a strike over layoffs that their union claims violated federal labor law, joining staffers at two theaters in New York that have done the same.

One hundred percent of participating staffers at the theater chain’s Sloans Lake location voted on Feb. 5 and 6 to greenlight the potential work stoppage. Days earlier, the chain laid off 47 out of nearly 300 workers across three Colorado locations, a move that Denver-based Communications Workers of America Local 7777 — which has a certified union in Sloans Lake — claims is illegal. The Cwa Local is also attempting to organize theaters in Littleton and Westminster, Colorado; the fate of those drives will be determined by ongoing proceedings at the National Labor Relations Board.

Local 7777 president Anthony Scorzo argues that the company didn’t conduct the layoffs lawfully while it was negotiating a first labor contract at Sloans Lake. “We...