Union leaders for the city’s office-building workers are warning that if they don’t reach a new labor pact by tomorrow night, they could strike on New Year’s Day, with workers in a dozen other cities joining in.

Janitors and other workers in 1,500 commercial buildings have authorized a strike if they don’t reach a new deal with building owners for the union’s 22,000 members.

Top pay for the building workers is now about $47,000 a year.

Janitors in other cities have stated their intention to honor picket lines if the strike spread to their buildings.