The families handed over the petition on Tuesday.
They held a press conference on the steps of City Hall, where several relatives of those killed in the attacks voiced their objections to Mamdani attending the solemn ceremony.
The petition was launched on Change.org on July 9 by 9/11 widower Giovanni Galante, whose wife, Grace, was killed in the attacks.
Galante said he started the campaign because of concerns over Mamdani's public positions, rhetoric and political associations.
'Ceremony should remain focused on victims'
Addressing the gathering, Galante said the families wanted the anniversary to remain centred on those who lost their lives and the survivors.
“The main purpose is just that we don’t believe in what he believes in, and we really want to be left alone,” Galante said.
He added that the 25th anniversary should give families and survivors a chance to remember and pray, rather than become the focus of a political controversy.
“This 25th anniversary is for our victims and us survivors to blend in and pray [on] that day for all the families, not have a circus around us,” he said.
Monica Iken, whose husband Michael was killed in the World Trade Centre, also spoke at the press conference and said the wishes of 9/11 families should be respected at the memorial site.
“If the families really feel that we don’t want someone at our world-class memorial museum that’s sacred and hallowed, we feel that that person should respect our wishes,” Iken said.
'Objection is not about religion'
Several speakers stressed that their opposition to Mamdani's presence was linked to his political positions rather than his religion or background.
Iken said the families' concerns also stemmed from the mayor's age and circumstances at the time of the September 11 attacks.
“It’s nothing against the mayor - it’s just against the fact that we feel he wasn’t even here. He was 10, he wasn’t in this country, and I think he should really respect us,” she said.
Cheri Sparacio, whose husband Tom was killed in the South Tower, similarly sought to distinguish the petition from any objection based on Mamdani's faith or origins.
“Our petition is not about Mayor Mamdani’s religion or where he came from; it is strictly about the policies that he has today,” Sparacio said.
City council members join call for Mamdani to stay away
The families were joined at City Hall by elected officials and organisational leaders who backed their demand.
City Council Member Joanne Areola criticised the administration and alleged that Mamdani had surrounded himself with individuals who hold views about the September 11 attacks that the families find offensive.
Areola said the mayor “does not care about 9/11 or the tragedies that took place because he surrounds himself with people who believe that America deserved what it got.”
City Council Member Vicky Paladino used stronger language in opposing Mamdani's planned attendance.
“I am not asking politely for the mayor not to come to that ceremony. I am asking, I am demanding that he not show his face at that sacred ground,” Paladino said.
Mamdani confirms plans to attend memorial
The families' press conference came a day after Mamdani spoke to ABC News about his plans for the 25th anniversary.
Mamdani said his focus would remain on the victims, their families and the first responders who responded to the attacks.
“I want this week to be a focus on the families whose loved ones were stolen from them 25 years ago in the horrific act of terror on September 11 - and a focus also on the first responders, everything they did for the city, and to the people who came together to try and help their fellow New Yorkers,” Mamdani said.
The mayor also confirmed that he intended to attend the memorial ceremony at the World Trade Centre site.
“And so, in the days to come, my focus will be on attending events that memorialise that incredible courage, and I will be there on Friday at the memorial just as I was last year,” he said.
The dispute comes as New York prepares to mark 25 years since the September 11, 2001 terrorist attacks, which killed thousands of people and left a lasting impact on the city and its residents.