Post Office managers are to take their first industrial action in 34 years in a dispute over pay.
The Unite union, which represents 900 managers, said its members will ban overtime and work to rule for 24 hours on Friday.
The union accused the Post Office of "dragging its feet" for 16 months over a pay deal and warned of further industrial action if the dispute is not resolved.
National officer Brian Scott said: "Unite members will not undertake any overtime, will refuse to work any additional hours or do work not proper to their role in the organisation. They will also refuse to travel outside of their working time, nor will they work in a location other than their normal place of employment.
"This is an important day for Unite members in the Post Office. They are keen to impress upon their employer their dissatisfaction with the failure to reach a pay agreement with the union and see this an opportunity to protest.
"No-one wants to take this action, but the intransigence of the employer makes this necessary."