Organizers say that between 2,000 and 3,000 unionized office cleaners will rally in Center City on Wednesday.
The rally will begin on the 2100 block of Chestnut Street, where about a dozen unionized workers were fired after the building was sold.
Greystar, the property management firm that took over the building and hired non-union janitors, did not immediately return a call for comment.
The firings have created a rallying point among unionized workers in the service sector in Philadelphia, where the union's contract expires Oct. 3. Contracts for 75,000 property management workers up and down the East Coast are set to expire.
The workers will march from 21st and Chestnut to Love Park. Democratic mayoral nominee Jim Kenney is expected to make an appearance.