Workers at Royal Mail have started strikes following a disagreement over cuts to jobs and services.
The strikes will run on selected days between 17 and 24 August.
They have already begun in Coventry, London, Leamington Spa, Nottingham and Stoke-on-Trent and will continue across the UK.
The union says Royal Mail is failing to invest in modernisation and is cutting jobs without agreement. Royal Mail says the union opposes necessary changes.
This phase of strikes comes before the the Communication Workers Union (CWU) aims to issue a national ballot in September on industrial action.
It has argued that the reduction in jobs would compromise the quality of services provided.
A spokesperson for CWU told the BBC said there were differences over what each side saw as modernisation, hence the recent deadlock in talks.
The shift online for some services, such as banking, had reduced some traditional mail, but on the other hand, people were shopping far more online, so more packages were being delivered, she explained.