Drugs are rife in many prisons and the action came after a watchdog warned on Thursday of a “dangerous lack of control” at HMP Bedford.
General Secretary of the Prison Officers’ Association Steve Gillan said prisons minister Rory Stewart “recognised that our concerns are justified and need addressing”.
Mr Stewart had earlier branded the protest “illegal” and judges warned trials were halted because defendants could not be brought to court from custody.
Justice Secretary David Gauke said: “We have to take steps to reduce the violence. I agree with those who say that the level of violence is unacceptably high.
“But action of this sort does nothing to help that process, and locking prisoners up for 24 hours a day, which may be the consequence of what the POA are doing, increases the risk of violence.”
Mr Gauke risked “inflaming” the row ahead of talks on Monday, Mr Gillan said.
At least 5,000 prison officers protested from 7am in car parks and outside entrances.
But following talks between ministers and union chiefs, staff returned to work early in the afternoon.
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