The bitter dispute between crown post office workers and management shows no sign of ending as Scottish staff walk out, followed on Tuesday by workers in England, Wales and Northern Ireland.
The 4,000-strong strike by members of the Communication Workers Union follows a UK-wide walkout on Saturday and is over plans to franchise or close more than 70 Crown post offices, the larger high street branches owned by Post Office Ltd.
The union says the franchise plans will lead to 1,500 job losses and much poorer customer service.
The walkout in Scotland will hit post offices in Edinburgh, Aberdeen, Dunfermline and several other towns. It is the eleventh since March and the CWU said it had no choice but to continue if an agreement could not be reached.
Several local councils have voted motions against the closures, including Manchester city council and Hastings borough council.
The CWU's deputy general secretary, Dave Ward, said: "The message can't be much stronger to Post Office management.
"Crown post office workers do not agree with management's slash-and-burn approach and are prepared to take prolonged industrial action to defend jobs and services and win a fair pay rise.
"This is a company which made £94m profit last year and paid out £15.4m in bonuses to senior managers It's a clear case of double standards and trampling those at the bottom for the benefit of those at the top."
Kevin Gilliland, network and sales director at the Post Office, said: "This action can only cause disruption to customers, cost our people money and place further pressure on the crown network which is currently losing £37m a year.
"We must continue with our plans to turn around the crown network to ensure we keep these branches on high streets and in city centres across the UK.
"We remain open to discussions with the CWU on pay options which do not add to the current loss of public money."
The state-owned Post Office receives £1.3bn of taxpayer subsidy. It says franchising out its branches to retailers is essential for its future. It is a separate company to the Royal Mail, which is due to be privatised before the end of the year.