Family members of the victims killed in the September 11, 2001 terrorist attacks have scheduled a demonstration for this weekend to protest a plan to relocate unidentified remains at the site underground.

New York City officials announced that they plan to move the unidentified remains from the Office of the Chief Medical Examiner on the East Side of Manhattan to a tomb beneath the National September 11 Memorial Museum, which stands where the twin towers once were. A group of relatives has criticized that plan, asking that the remains be moved instead to an above-ground space in the 9/11 memorial plaza.

“Let us have a voice! Let us have a say!” Jim Riches, a retired firefighter whose son was killed in the terrorist attacks, told the Associated Press. “We are outraged and we will never rest until our loved ones, America’s heroes, rest in peace.”

The remains, including approximately 7,930 body parts, will be moved Saturday in a solemn procession of New York City police officers and firefighters. Once there, they will be put into a specially designed burial vault at the bedrock level. The entire process will be overseen by the medical examiner, who hopes that new technology will eventually help officials determine the identities of the remains.

Still, family members say they are not looking forward to the museum’s opening, scheduled for May 21.

“It’s a day of sadness and a day of outrage,” Sally Regenhard, the mother of a fallen firefighter, told the AP.

City officials maintained that they checked with family members before deciding on a plan and said that relatives have had opportunities to contact the city, either to complain or request more information. The problem, critics say, is that the city only consulted a fraction of the victims’ families, perhaps with the aim of intentionally distorting the result.

“The city won’t do a survey because they know we’re right, that the majority of family members would say no,” said Norman Siegel, a civil rights attorney who represents the families opposed to New York’s plan.

The AP obtained a memo written by a member of the Mayor Michael Bloomberg’s administration revealing that a process was in place to inform family members about the plan and that the administration intended to carry out the relocation without informing the public. Shortly after Mayor Bill de Blasio was sworn in, his administration went public with the plan to transfer the remains.

Word of the protest surfaced just days after a sad milestone. The names of twenty new police officers were added to the New York State Police Officers’ Memorial, including 13 who passed away in recent years due to illnesses that were the result of rescue and recovery efforts in Lower Manhattan. That increased the number of officers who died from cleanup-related illnesses, more than the 60 policemen who were killed in the attack.