Mayor-elect Eric Adams reiterated his call for punishing detainees at Rikers Island and other city jails who commit violence by locking them in solitary confinement, triggering outrage from activists and defense attorneys who see the practice as harmful and a perpetuation of humanitarian abuses at Rikers Island.

Adams’ announcement comes as Mayor Bill de Blasio’s administration works to end solitary confinement, or punitive segregation, by the final day of the mayor’s term on December 31st.

“They better enjoy that one-day reprieve because January 1st they are going back into segregation if they committed a violent act,” Adams said to laughter from an audience that included correction union officials attending a press conference on Thursday.

Adams likened solitary confinement as jail for those who are already jailed. “While you’re in jail, you commit a slashing on an inmate, [and] you don’t go to jail?” he asked. “I mean this is not making any sense. If you say to a violent person that slashed an inmate that nothing is going to take you out of [general] population so you don't slash other inmates, that sends a terrible message.”

Without citing specific policies or practices, Adams said he envisions “segregation without it being inhumane,” and not like “going back to the days of being in the hole.”

Adams was speaking at a press conference announcing a new commissioner for the Department of Correction, Louis Molina, who first mentioned the new policy.

“We have record-setting inmate-on-inmate assaults,” Molina said. “We have staff being assaulted on the island. There are violent people — a percentage on Rikers Island. And we need a method and restrictive housing solution for them in order to make sure that they don't hurt or injure anyone else."

The Legal Aid Society, which represents inmates at the city jails, said Adams’ plan “throws away years of progress undoing the physical and mental harms caused by solitary confinement.”

“It reveals the administration’s intent to reinstate regressive and violent policies over modern and more effective practices,” the group said.

Also condemning Adams on Thursday was the sister of Layleen Polanco, a transgender woman suffering from epilepsy who died in a solitary cell that she was sent to for her alleged role in an altercation.

“If you want to continue to use solitary confinement, it means you are ok with people dying and people being tortured,” said Melania Brown, Polanco’s sister, in a statement. She advocated for “alternative forms of separation.”

Sociologists and criminal-justice reform advocates describe solitary confinement as a public health issue. Earlier this year a study from Cornell University showed that inmates who were in solitary confinement while incarcerated were 60% more likely to die within five years of their release than others who were formerly incarcerated, while controlling for age, race, and other factors, such as the reason for their convictions.

State Senator Julia Salazar said the announcement indicated that Adams didn’t understand what was happening at Rikers. “Solitary confinement is harmful, and it does not even do what its proponents want it to do: reduce violence or correct behavior,” Salazar tweeted. “It makes things worse.”

In recent years correction officers at the city jails have increasingly relied on solitary confinement, also known as punitive segregation, to punish inmates involved in violence as the jails have become deadlier and bloodier.

De Blasio announced a plan earlier this year to dramatically limit isolation, allowing detainees to spend hours outside of their cells and to socialize with others. Citing correction officer staffing shortages, he has repeatedly put that on hold, but in recent days efforts have ramped up to move all detainees from solitary confinement to the general population by the end of year.

In 2015, de Blasio ended solitary confinement for those aged 21 and younger. Solitary confinement is also not an allowable punishment for pregnant women and those with serious mental illnesses. And he had pledged to end it entirely by the time his term ended.

Meanwhile, a bill to ban solitary confinement is also sitting in the City Council with broad support, but no vote is scheduled before the current term ends this month.

New York State enacted a law in April to end solitary confinement lasting more than 15 days and barring younger people, older people, and those with disabilities from being subjected to such confinement. But the law doesn’t take effect until March of next year.

There have been several high-profile cases of detainees dying after spending time in solitary confinement, including Kalief Browder, who committed suicide after spending two of his three years in solitary confinement while awaiting trial for stealing a backpack.