The work stoppage — as well as the picketers’ loud chanting and pot-clanging in front of some of the city’s largest hotels — comes at a busy time for Chicago tourism. The city had a record 55.2 million visitors last year, according to the mayor’s office, and hotel room revenue in the central business district was up 11 percent through August of this year compared with the same period last year, according to hotel data specialist STR.