A town centre Post Office in South Tyneside was closed due to industrial action.
The Crown office in Keppel Street, South Shields, was one of more than 100 branches which were shut nationwide on Thursday due to postal workers striking over job and pension disputes.
Customers were informed by a poster and were advised to visit one of five other branches in the borough instead.
Members of the Communication Workers Union (CWU) and Unite walked out in protest at the closure of offices, job cuts and changes to the pension scheme.
A total of 118 out of 305 branches were closed nationally. But the Post Office said almost 99% of its 11,600 sites remained open.
Dave Ward, general secretary of the CWU, said the Post Office was at “crisis point”, and urged the Government to stop the “cycle of closures, job losses and attacks on workers’ terms and conditions”.
Customers were advised to attend branches in Frederick Street, Stanhope road, Prince Edward Road, and Horsley Hill Square, all South Shields, plus Bede Trading Estate in Jarrow.
The unions also warned of further action, although talks aimed at resolving the row are planned next week.
Kevin Gilliland, the Post Office’s network and sales director, said: “We apologise to any customers who have been inconvenienced by the disruption to service in a very small number of branches.”
He added: “We are making steady progress to modernise the UK’s biggest retail network. These changes are needed to make our services better for customers and ensure that Post Office branches thrive at the heart of communities for future generations. In just over three years the Post Office has modernised over 6000 branches, leading to improved facilities and more convenient and accessible services for customers.”
Mr Gilliland said the Unions’ comments regarding the business’s performance are misleading and stressed that people across the business continued to be kept fully informed of any changes that might affect them,