Newly-elected Unite leader Len McCluskey is to speak in support of keeping the postal service public at a rally in central London today (Wednesday).
The event is organised by the Communication Workers Union (CWU) which represents the vast majority of workers at privatisation-threatened Royal Mail.
Unite covers management grades - and co-operation between the two groups is rare.
The rally is from 11am - 2pm at Central Hall, Storey's Gate, Westminster, London, SW1H 9NH.
There is a long list of speakers.
After the rally supporters of the Keep the Post Public campaign will lobby members of parliament.
Opponents of privatisation can find a model letter to write to their MPs.
DECLARATION: I'm doing freelance work for the CWU and will be reporting from the rally on the union website.
MINUTE BY MINUTE: Keep the Post Public rally coverage
AS IT HAPPENED: Keep the Post Public demo and rally