Thousands of postal workers in London are to hold fresh strikes in a row over jobs and services.
The Communication Workers Union said action would be taken by delivery staff on 8 July, distribution workers on 9 July and mail centre staff on 10 July.
The union claims Royal Mail is cutting jobs and services but failing to modernise the business.
Royal Mail said the strikes would only halt existing efforts to modernise the service in London.
A Royal Mail spokesman said: "Customers will not understand how the union can claim to support modernisation but then announce strike action to halt existing efforts to modernise Royal Mail in London.
"The CWU's strike action can only hurt customers and drive them away, particularly in the vitally important online fulfilment and packets areas - which are crucial to securing a successful future for the business and its employees - but where large customers have a real choice to use other operators."
This latest announcement comes after up to 8,000 CWU members in London and about 160 in Scotland held a two-day strike on 19 June over the same issue.