Jones is one of 3,000 workers who clean and service about 120 office buildings in Center City and University City, including the FMC Tower, the Comcast towers, and the Peco building. The workers, largely African Americans or immigrants, have been union members for nearly a century, making them among the first low-wage service workers to be unionized in the city. They have been able to transform these jobs into what’s become a rarity: the service job you want to hold on to. The average cleaner makes $17 to $19 an hour, has a pension, and doesn’t pay premiums for good health insurance.