Industrial action
Members of Napo, the probation service union, voted to refuse overtime from 23 November and could take strike action should the union "deem that option to be necessary".
Napo general secretary Ian Lawrence said the service was "already in crisis" before the early release scheme came into force, which relies on probation staff monitoring freed prisoners in the community.
The union said it launched its ballot because of an "inadequate" 5% pay offer from ministers and a failure to cut workloads. Napo had sought a 12% increase.
On pay, Napo members voted by 85% in favour of action short of strike action and 74% in favour of strike action. In a ballot on workloads, the vote was 87% in favour of action short of strike action and 75% in favour of strikes.