Rural post offices could be next in the firing line after plans to shut one in five High Street branches were announced, it is feared.
The Post Office has revealed plans to seek partnerships with retail firms for 70 of its 373 Crown Post Offices because it is losing £40m a year.
Unions admit they are "bemused" as to why none of the 16 branches in major towns and cities across the region featured on the hit list.
But they say the flagship Post Office "transformation project" is failing to persuade sub-postmasters in the region to volunteer to adopt new working practices.
The Communication Workers Union claims it is "only a matter of time" before smaller branches are forced to become one of the new main or local offices.
And this could see "fortress" counters scrapped and customers deprived of their privacy as they are forced to queue up at shops and petrol stations and conduct their business in public.
Chris Roche, South West spokesman for CWU, said: "They are trying to get postmasters to sign up for a new contract which will hit them in the pocket – pressure is being brought but they are not signing up.
"The network as a whole faces an uncertain future and these new local offices will be very basic, open for longer hours but not doing the same job.
"It is hard to see the scheme remaining voluntary indefinitely and it is only a matter of time before they force the issue."
Staff were said to be "in shock" after the Post Office announced their plans for Crown branches, a move it denies is a closure programme. The company say the move will help the offices, based mainly in high streets or busy shopping centres, remain in their current locations, pledging no compulsory redundancies.
There was uproar in the region just over five years ago when a massive wave of post office closures was announced by the Labour government.
Plans to axe 2,500 branches across the country and up to 100 in Devon and Cornwall prompted Westcountry MPs to demand a "people's revolt" to block the plans.
Since then many towns have lost branches and villages have been left with no service at all or in some cases limited services provided in local shops. A number of the larger Crown offices, which are owned by the Post Office, have closed with services transferred to WH Smith and Co-op stores.
The Post Office said it was seeking to link up with national partners or local, independent firms, adding that if it could not find a suitable deal, the Crown office will remain. It said in a statement: "We are currently undertaking the biggest business transformation programme in the history of the Post Office.
"Our investment will maintain the size of the network and modernise branches to meet customer needs.
"Crown branches are a fundamental part of our long term growth strategy and need to be brought into profit."
The CWU partly blames the Government for failing to deliver extra services to help keep branches afloat.
General secretary Billy Hayes said the announcement was a "huge blow" to the Post Office network, saying: "Staff will be in shock at the scale of what will effectively be the closures of Crown post offices across the country.
"This move will have a huge impact on the high streets of small towns earmarked to lose their Crown post office.
"These offices provide a dedicated specialist service to communities, which will not be replicated by a window or two in a bigger shop.
"We've seen problems with access to Post Office services in previous franchise arrangements and this could create further barriers to accessing a range of Post Office services.
"It leaves huge questions about how it can realistically deliver services for passport applications, identity services and a range of financial services, while being dramatically pruned back."