The tribute is one in a series of national events designed to commemorate the 9/11 terrorist attacks.
Giuliani, whose campaign took heat last week for a California fundraiser during which volunteers asked that donors contribute $9.11, is scheduled to speak at 4 p.m. at Congress Hall in Cape May.
The demonstration, said union spokesman Jeff Zack, is part of the organization's nationwide effort to question Giuliani's 9/11 "hero" credentials, which form the backbone of his campaign.
"We'll continue to focus on high-profile events where it is relevant for our members to go and say their personal opinion of Giuliani," Zack said. "Anytime an event has something to do with either 9/11, or first responders, or anytime he's in New York City, we'll be there."
The union has claimed that Giuliani failed to replace firefighters' faulty radios in the years leading up to the attack, suspended the search for remains at ground zero too soon, and erred in locating the city's emergency command center in the World Trade Center complex.
However, not all firefighters agree with the union's characterization of the former mayor.
"Mayor Giuliani provided much-needed leadership during our city's greatest crisis, and not a day goes by where he doesn't think about the terrorist attacks from six years ago," said Howard Safir, chair of First Responders for Rudy.
By Liz Halloran