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.
More top news
Thousands of pounds worth of heroin has been found stashed inside the covers of children's books at Heathrow Airport.
Internet search engine says Cilla Black was the subject of more online searches than Kim Kardashian this year, beaten only by Taylor Swift.
A supermarket price war and fierce competition across the rest of the high street has seen shop prices slumped by a record level last month.