California authorities have won court approval to force-feed some prisoners on hunger strike.
Officials had voiced concerns that inmates may have been coerced into refusing food in a protest against the state's solitary confinement policies.
US District Court Judge Thelton E Henderson ruled that California prison doctors may force-feed select inmates near death, even if they had previously signed orders asking not to be resuscitated.
Around 136 California inmates are currently taking part in a hunger strike that began on 8 July in prisons across the state.
They are demanding an end to a policy of housing inmates believed to be associated with gangs in near-isolation for years.
So far, 69 of the striking inmates have refused food continuously since the strike began.
This is the second time prisoners have launched a hunger strike to protest at the state's practice of housing some inmates for years in its four Security Housing Units.
About 4,500 prisoners were housed in the units when the strike began, officials said.
State officials said the units are needed to stem the influence of prison gangs and administrators have repeatedly characterised the hunger strike as a power grab by gang leaders.
But the state's policy of housing prisoners for years in these units has been condemned by a number of human rights organisations, including Amnesty International.
At least one prisoner on the hunger strike has said that he is willing to die to make his point that the detentions are inhumane.
The hunger strike is the latest problem to plague the state's prison system, which is under federal court order to reduce crowding by the end of the year, possibly by releasing up to 10,000 inmates early.
The hunger strike launched last month has already gone on twice as long as a similar protest in 2011 and has attracted more prisoners - 30,000 at its peak - although numbers have since dramatically dwindled.
Now well into a second month without food, dozens of inmates have been sent to hospitals, officials said.