A Belfast subpostmistress has accused the government of "eating away" at the income of post offices "by stealth".
The number of post offices fell by more than 4,000 since 1999
Wendy Cairns, who runs Dunmurry sub post office, is among those calling for urgent action to safeguard the network of rural post offices.
A petition of four million names will be handed into Downing Street and the National Federation of Subpostmasters will hold a rally in London.
Ms Cairns said when post offices close "communities just die".
Ms Cairns has run the sub post office in Dunmurry for eight years and her father ran it for nearly 50 years.
"We'd like the government to undertake an assessment of the social and economic role played by post offices in communities right across the UK and for them to provide ongoing support to the non commercial parts of the network," she told BBC Radio Ulster.
"We'd like a network that is viable, a network that isn't subsidised totally.
"We want the work and we want to do it well and we want to serve our customers. We are a part of a community.
"In many places when the post office closes, the community loses its heart, the people don't come down to the towns and villages... and the communities just die."
The post office network is losing £200m a year and the government is widely expected to require some closures as part of a subsidy renewal agreement.
The government says the 800 smallest post offices are used by an average of 16 people a week, and that the rural network is currently supported by an annual subsidy of £150m.
The number of post offices has fallen from 18,393 in 1999 to 14,376 in 2005, according to Postwatch, the postal services watchdog.
It is understood Ms Cairns and other people who run post offices in Northern Ireland are to meet a number of the province's MPs about the matter.
Ms Cairns said: "We feel like we are losing all roads and directions."
Among problems faced by post office income is the planned withdrawal of the Post Office Card Account, used by millions to access pensions and benefits.
Almost 400 MPs have signed an early day motion calling for that decision to be reversed.