Probation and family courts staff have voted in favour of strike action over pay and workloads.
Members of the National Association of Probation Officers (NAPO) backed industrial action, including a total ban on overtime, which will start on 23 November.
And although NAPO's leadership has not decided to walk out just yet, plans are being made to launch strike action at a later stage if they "deem that option to be necessary".
The ballot was launched last month following what NAPO called an "unacceptable" 5% pay offer from the government, with members performing "thousands of hours of unpaid overtime" to meet "the demands placed on them".
The union says these workload concerns have only increased since the government launched its early prison release scheme to ease overcrowding.
NAPO general secretary Ian Lawrence said: "The high turnout by our members, and the result, vindicates the campaign to achieve a pay rise to make up lost ground in comparative pay with other staff employed within HMPPS (His Majesty's Prison and Probation Service).
"The vote also reflects serious anger at the state of probation workloads, which were already in crisis before the latest version of the prisoner early release scheme.
"Our members have tried desperately to do what the previous government, as well as this one, have demanded, but have done so against a background of inadequate staffing and a lack of resources within our communities to provide rehabilitation as an alternative to re-offending."
The union says that probation wages have stagnated since 2010, with reception staff on a salary just above the minimum wage.
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On pay, 86% of Napo members voted in favour of action short of strike action (working to contract) and 75% in favour of strike action.
In a ballot on workloads, the vote was 87% in favour of action short of strike action, while 76% supported strikes.
Sky News has approached the Ministry of Justice for comment.
(c) Sky News 2026: Probation staff vote for strike action in 'serious anger' over pay and workloads
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