SAN FRANCISCO — Corrections officials in Sacramento said Thursday that they would discipline inmates who participated in a renewed hunger strike to protest conditions in the state’s highest-security prisons, where some prisoners have been held in virtual isolation for decades.

More than 4,200 inmates at eight prisons have been refusing state-issued meals since Monday, according to the California Department of Corrections and Rehabilitation. The hunger strike, the second this year, is the latest problem to face state prison officials, who are under a Supreme Court order to reduce the state’s prison population by more than 30,000 people.

A memo was distributed to prisoners at the state’s 33 correctional institutions warning that if they took part in the hunger strike, they would be subject to disciplinary action that could include confiscation of canteen items like food they had bought.

Prisoners identified as leaders of the strike would also be removed from the general population and “placed in an administrative segregation unit,” according to the memo.