The move was a blow to civil liberties advocates in New Jersey, who point to a national reform movement that has led to limiting the practice, also known as isolated confinement, in several states.
The measure sought to require prisons and jails to use isolated confinement only as a last resort, restricting its use to 15 consecutive days or 20 days in a two-month period.
It also sought to ban the practice for inmates who are mentally ill, pregnant or have other special needs, requiring daily medical evaluations for prisoners in isolation.