Changes to the Minimum Practice Income Guarantee (MPIG) will hit the most vulnerable rural residents, warned Action with Communities in Rural England (ACRE).
The national voice for England's network of rural community councils is calling on the next government to reinstate the funding in its ACRE 2015 election manifesto.
ACRE head of rural insight Nick Chase said: "The loss of any surgery in an isolated rural area will cause hardship to elderly and vulnerable residents.
"Rural communities are home to 25% of all older people and with the percentage of over-85s set to double in the next 20 years, provision of local healthcare for our ageing population is crucial.
"The closure of surgeries will pose problems for older people who may face difficulties in getting to appointments further afield."
In rural areas, 35% of pensioner households have no access to a car.
Mr Chase said: "With cuts in public transport, they are often forced to rely on friends, family and overstretched volunteers."
MPIG is a top-up payment given to some general practices since 2004.
In 2014/15, NHS England began a seven-year plan to phase out the payment in a review of how GP surgeries are paid for their services.
The move led to widespread objections from GPs and the British Medical Association.
Mr Chase added: "ACRE is calling on the next government to reinstate MPIG for rural surgeries."
An ACRE survey in 2014 showed that the withdrawal of MPIG would hit rural GPs hard. In Devon, it found that at least 10% of rural surgeries faced closure. In Cornwall, it found that 20% would lose significant income if these changes went ahead.
Mr Chase said: "While there are those who say that the MPIG is inequitable and requires a rethink, the entire withdrawal of the funding is not the way forward.
"The number of GP surgeries closing has increased significantly over the past 12 months. NHS England is aware of 98 surgeries that could face closure as a direct result of withdrawal of MPIG."
South Lakes MP Tim Farron presented a Bill to Parliament to require the provision of GP surgeries in certain rural areas on 21 October 2014. This bill is due for a second reading on 6 March 2015.