Staff at the Royal Mail depots in Montpelier and Whitehall are striking today, with no mail due to be delivered within the BS5, BS6 and BS7 postcode areas, including Redland, Bishopston, Horfield, Easton, Redfield and St George.

And postal deliveries across almost all of Bristol could be hit next month if ballots under way at 13 depots lead to more strike action.

The Post reported yesterday that workers at the Yate, Keynsham and Portishead depots had also voted for strike action, which is due to take place early next month.

The Communication Workers Union says workers at 13 more depots are being balloted, with the results of their vote likely to be known between July 28 and 31. Any strike action could then be co-ordinated with the three depots which have just voted for action.

The depots going to ballot at the end of the month include the regional processing centre in Filton, the delivery centre in Severn Beach, the South and South Eastern delivery offices in Bedminster, the City delivery office in Easton, as well as offices in Clifton, Kingswood, Nailsea, Patchway, Westbury-on-Trym and Axbridge.

CWU Bristol and District branch secretary David Wilshire said: "We would be looking to co-ordinate any strike action from these depots with Yate, Keynsham and Portishead and this would take place early August.

"We have also put in ballot requests for Avonmouth, Fishponds and Weston-super- Mare, but the results of these would be known too late to join in these strikes and so they would be timetabled for later."

Postal staff are striking over proposed job cuts.

Kevin Beazer, regional secretary of the CWU, which has its head office in Lawrence Hill, said the decision to take industrial action today was not taken lightly.

Mr Beazer, who lives in Downend and used to work at the sorting office next to Temple Meads station before becoming a full-time union official, said: "There are serious and growing problems in the postal sector which urgently need resolving.What we are doing is trying to protect jobs. Royal Mail's cuts will take hundreds of jobs out of offices. And the people who will be left after the cuts will be picking up the work of those people for no more pay... but we are not just protecting our members' jobs, we are trying to protect the services that Royal Mail offers as well."

The 170 postal workers on strike in Bristol today, 70 at Whitehall and 100 at Montpelier, will be joining thousands of colleagues across the UK who will be striking and demonstrating today.

Royal Mail has condemned the CWU's plan for today's strike action.

A spokesman said: "Royal Mail will be doing everything possible during the strike to provide as complete a service as possible to customers."

"Strike action hurts both businesses and individuals and our customers will not understand how the CWU leadership can keep saying it backs modernisation while constantly resisting the introduction of new technology and more efficient working practices on the ground.

"We are again urging the CWU to work with us to implement that agreement and help complete the transformation of Royal Mail in all our interests.

"Royal Mail is already half way through that transformation - and has already invested more than £800m - but we must up our pace in the face of dramatic and accelerating changes in the market in which we operate."

This afternoon, a letter and postcard will be delivered to Royal Mail's chief executive Adam Crozier, and Business Secretary Peter Mandelson.

Once these have arrived safely at their addresses a national balloon release will take place with thousands of balloons rising above Royal Mail workplaces across the UK.

Lord Mandelson has recently made clear his view that the union is "essentially boycotting the agreed processes for making change in the Royal Mail" and that the union must change its attitude to change and implement the 2007 agreement on Pay and Modernisation.