Organizers of the coalition said a candlelight vigil will be held at the site of the proposed project on Sept. 10 -- the eve of the ninth anniversary of the terrorist attack that killed almost 3,000 people and destroyed the World Trade Center twin towers.
Opponents of the project object to its proximity to Ground Zero.
Talat Hamdani -- whose son Salman, a New York City police cadet who was killed while responding to the attack -- told CNN the issue "is not about location. It is about our rights as Americans."
"All those people who died that day ... they were murdered for being Americans," Hamdani said. "We should honor those people who were murdered that day by living up to America's core values."
Debra Burlingame, whose brother was the pilot of the plane hijacked by terrorists and crashed into the Pentagon Sept. 11, 2001, said the Islamic center is "nothing short of a provocation, an insult to the families of people who were murdered, whose bodies were scattered all across that site."
New York Mayor Michel Bloomberg Tuesday reiterated his support for construction of the center.
"We are Americans, each with an equal right to worship and pray where we choose," he said. "There is nowhere in the five boroughs of New York City that is off limit to any religion."