Probation staff working for community rehabilitation companies have announced a walkout.
The three-hour strike will be followed by two and a half weeks of work to rule action by the employees.
The Unison-organised move is the second strike this summer, following one on July 14.
Members are protesting against a zero per cent pay rise offer. It is the fourth year in a row that they have not seen their remuneration increase.
National officer Ben Priestley (pictured) said: "The first strike sent a very clear message to the employers that Unison members are serious about getting a decent deal on pay for 2014.
“By taking this further three-hour strike and following it with action short of strike, we want to show them that they must come back to the negotiating table.”
Community rehabilitation companies were introduced in February, introducing private companies into the running of low to medium risk probation services.