More than 1,100 union workers at DHL’s air cargo hub at the Cincinnati/Northern Kentucky International Airport walked off the job Thursday, a move that affects one of the parcel carrier’s largest logistics facilities during the busiest shipping season of the year.

The International Brotherhood of Teamsters said its members are protesting unfair labor practices at the hub run by DHL Express, a U.S. unit of German logistics giant Deutsche Post that handles express parcel business.