Thousands of workers will stop working at lunchtime and picket outside their branches, following a day of similar industrial action on March 30th.
At present, the Post Office organisation is haemorrhaging £40m a year through its 370 “crown” offices, and as a result is planning to move 70 of its high street stores into other local retailers, to try and stem company losses.
According to the company, 97% of its operations would operate as normal, but the Communication Workers Union (CWU) says that hundreds of jobs will affected by the changeover.
Crown offices are the bigger branches directly run by the company, rather than the smaller high street sub-offices handling, according to the CWU, around a fifth of all company business and 40% of financial service sales.
CWU general secretary Billy Hayes said in a statement that the closures amounted to “a desperate attempt to slash costs to meet government funding cuts by 2015".
"But the reality is that these are euphemisms for closing offices, drastically altering the make-up of the Post Office network and handing the running of services over to corporations which are built around other income streams and could walk away from Post Office services,” he added.
Kevin Gilliland from the Post Office told the BBC that he regretted "any inconvenience that may be caused by any strike action".
He added, "Through our critical modernisation plans we intend to turn this part of our business around and keep Post Office branches on high streets across the UK. Any move to a retailer's premises would offer access to the same range of Post Office products and high levels of customer service in a new modern branch."