Small businesses have reacted angrily to the government's plans to shut 2,500 post offices due to rising losses.
Campaigners fear for rural communities, businesses and the vulnerable
The Federation of Small Businesses described Trade and Industry Secretary Alistair Darling's announcement as "post office carnage".
The Commission for Rural Communities welcomed the consultation but said it was also concerned about the impact on communities and vulnerable people.
Postal services watchdog, Postwatch, said the plan provided "clarification".
However, Clive Davenport, chairman of the Federation of Small Businesses (FSB), said: "This carnage on high streets across the UK is completely unacceptable and very short-sighted.
"Small firms employ 58% of the private sector workforce.
"We have to ask if it is sensible to put a large proportion of those 12m jobs at risk to save what is, in government spending terms, a small amount of money."
He also called for the proposals to "be reversed while there is still time".
Meanwhile, the Commission for Rural Communities (CRC) has emphasised that any changes "must not further marginalise the one-in-five rural people living in poverty".
Vulnerable groups in rural areas, such as older people, low-income families and those without access to a car, "rely disproportionately on post office services", it said.
Dr Stuart Burgess, chairman of the CRC, said: "Many shops and other services are linked with the post office in rural areas and we do not want changes to the post office business undermining other crucial rural services."
But Dr Burgess added: "The reorganisation and reduction in the number of post office outlets outlined today must build in safeguards for the most vulnerable people and identify other, creative ways of delivering postal services in rural areas."
Dr Burgess did welcome the "government's commitment to look at different ways of providing services" such as more mobile provision but called for other solutions like post offices in pubs and village halls to be supported.
Postwatch said that it had been urging the government to propose a sustainable way of meeting customers' post office needs for man than 12 months.
'Social and economic role'
Millie Banerjee, Chairman of Postwatch, said: "Today's announcement and consultation are the first steps in providing a clear view on how the post office network will look in the future.
"The focus should be on ensuring customers have access to post office services.
"Solutions will vary from location to location. But, for example, if a number of expensive-to-run, seldom used post offices can be replaced with a cost-effective mobile service that meets communities' needs - doesn't that make sense?
"We are pleased to see the government recognises the social and economic role of the post office network but are disappointed that there is no further information on how the social role will be taken into account when considering a post office's future."