By Matt Petrillo

PHILADELPHIA (CBS) — A massive crowd representing Philadelphia’s janitors gathered in Center City on Thursday. The workers are demonstrating for fair wages and better benefits.

The Office Cleaners Union is negotiating its contract in Philadelphia. The union represents 3,000 workers and many of them gathered for the demonstration.

“It’s hard work! It’s hard on your back and it’s hard on your knees,” Ellen Williams said.

Ellen Williams has been making sure the Wells Fargo Bank building at 5th and Market Streets has been spotless for more than two decades, but today she’s joining hundreds of Office Cleaner Union members to protest proposed cuts to some benefits.

“Whatever we have now, that’s what we need now,” Williams said. “The people that owns these buildings out here, they got money.”

These union members are wearing shirts that read “Our power is global.” The message refers to the several other cities represented by the Office Cleaners Union and where they say they won’t let anyone take away the benefits they fought for so long.

“These members have put many years into these buildings,” SEIU Mid-Atlantic District Leader Daisy Cruz said. “They want to be able to retire with dignity. They’re hard workers. They want to make sure they get what they deserve.”

Philadelphia Mayor Jim Kenney is joining the group at the end of the march by 18th and Walnut Streets at Rittenhouse Square. Union members say they are prepared to strike.