Hundreds of jobs will be lost if proposals to modernise Royal Mail in London go ahead, a union has claimed.
Under the plans two sorting offices, in south and east London, and a central London delivery office would close. It is not clear how many jobs would go.
The Communication Workers Union (CWU) said the move would affect more than 3,300 workers and damage services.
Royal Mail said it had more mail centres than was needed and no decision would be made until the New Year.
Unions are currently being consulted on the proposals to close sorting offices in Elms Lane, Vauxhall, south London, and Trees Crescent in east London, as well as Rathbone Place delivery office in central London.
Work would be transferred to Mount Pleasant sorting office in central London and other mail centres in outer London.
Accusing the Royal Mail of "industrial vandalism", the CWU said the plan was based on "asset stripping and the removal of full time mail centre jobs in London".
It claims the move had nothing to do with modernisation, quality of customer service, productivity or the welfare of employees.
The proposals are part of Royal Mail's investment and modernisation programme.
It is spending £2bn introducing new technology and equipment to provide "the most efficient and effective network for transporting the post".
Royal Mail said it expects that by 2014 the amount of mail posted in London will have halved since 2006 and the amount of mail being delivered to London addresses will have dropped by a quarter.
'Need to respond'
The organisation said it also planned to introduce new machines which would be able to process mail faster.
A spokesman said: "We need to respond to the huge growth in electronic communications and the resulting decline in overall mail volumes which in the UK means that there are now 13 million fewer letters posted every day compared to five years ago.
"Within this shrinking postal market we are also losing share to rival operators which now carry more than one in three letters and more than half of all business mail.
"Royal Mail has an excellent track record of supporting people through changes and we are committed to continuing this."