As many as 50 people have joined the picket lines. Wednesday was dubbed "family day" where spouses and children joined the workers, Wagner said.
Workers there belong to Teamsters Local 992, which represents 394 UPS workers there and at centers in Hagerstown and Chambersburg, Pa.
Hagerstown center workers, on the other hand, have said they are frustrated with the union.
They said they would like a chance to vote on the company's final proposal, which was rejected by the union's negotiating committee.
Frederick center workers said they are standing behind the union one hundred percent.
Jim Slabik, 30, said he can't stand by and watch more and more full-time jobs being converted to part-time.
"They're paying everybody a part-time wage and working them 40 and 50 hours," he said.
Slabik and a number of Frederick center workers live in Hagerstown.
Many transferred to Frederick when the center opened five years ago in order to move from part-time to full-time jobs.
"Everybody has mouths to feed, but you gotta take a stand every once and awhile," he said.
Today will mark Dennis Baker's 16th year with UPS.
"Personally, I think it would be hard to work for this company without a union," said Baker, 36, who lives in Hagerstown.