As Party City Holdco Inc. wades through bankruptcy, some of its most important vendors are banding together to negotiate better trade terms for a holiday the company relies on: Halloween.

Party City, the party and costume supply chain with more than 70 locations in California including several in Los Angeles, is shutting down operations immediately and laying off its employees.

SAN ANTONIO — Its a spooky time of year for Party City. Some of the more popular costumes are superheroes like Wonder Woman and Deadpool. Other top picks are characters from recent movies, like ...