Postal workers are striking for the second time in four days over a row about job and pay cuts.
The Communication Workers Union (CWU) says staff at Royal Mail's crown post offices are striking between 06:00 BST and 12:00 BST today in protest at plans to privatise 85 post offices to WH Smith.
On Friday postal workers staged their first 24-hour strike in more than a decade in a separate dispute.
According to the CWU, Royal Mail's privatisation plans will result in 1,500 job losses, with workers experiencing pay cuts of between £5,000 and £6,000 over the next three years.
The union also claims that pensions will be cut short by thousands of pounds, while Saturday allowances will similarly by hit.
"Members have been left with no alternative but to take strike action as management are steamrolling ahead with closures of crown post offices across the UK," said the union's national officer Andy Furey.
"The plans announced by Post Office Ltd will have an extremely negative impact not just on postal workers but also for the public."
A spokesman for Royal Mail said that the "vast majority" of crown post offices were operating normally, with only ten of its 465 network closed as a result of the strike action.
"More than 14,000 of the 14,200-strong network of post offices are open normally today. All deliveries and collections are running normally today and are unaffected," a statement elaborated.