The Post Office is planning to close and franchise 37 Crown offices, with loss of 300 jobs and 127 specialist roles, according to the Communication Workers’ Union (CWU).
It says the number of jobs lost since the beginning of last year is 2,000.
The union staged five days of strikes just before Christmas at the Crown post offices in a dispute that was partly about branch closures.
Crown post offices are the larger branches usually found on High Streets.
The union is also concerned about job losses and pension provision.
The CWU’s Dave Ward told the BBC at the time of the pre-Christmas strike that the government and the company would announce a further tranche of closures in January.
Mr Ward said: “Today’s announcement comes less than three weeks after the closure of a major government consultation on the future of the Post Office and sticks two fingers up to everyone who took part in this.”
The union said that 75,000 postcards had been sent by members of the public to the government calling for an end to the closure and franchise programme of the Post Office.
It added that the Post Office network has been reduced by more than 50% over the past 30 years.
In April 2016, the Post Office announced plans to transfer up to 61 branches into WH Smith stores over the following year.
It said the move was part of a 10-year plan to cut costs and save cash, and would act as a way of “safeguarding the future of the network”.