Michael Buchanan
Social affairs correspondent
The Samaritans are planning to close more than 100 branches across the UK and Ireland, the BBC has learned.
In a presentation to staff, the suicide prevention charity's chief executive said "at least half" of their branches will close.
Dozens of branches have voiced concerns, some fearing the proposals will lead to an exodus of volunteers: "They're dismantling something that has worked for 70 years," said one volunteer.
The Samaritans said having more than 200 branches "is not sustainable and hinders us" from providing the best service.
Founded in 1953, the Samaritans focus on preventing suicides by connecting trained volunteers with people who are struggling.
The charity estimates it answers a call for help every 10 seconds.
The proposals were revealed in a video message sent by the leadership of the charity to volunteers last week.
Chief executive Julie Bentley, said while there wasn't "a definitive view" on how many branches the charity needed: "It's likely that within the next seven to 10 years our branch network will have reduced by at least half.
"With less branches, we'll look to move to fewer but bigger regions," she added.
If the charity's board agrees to the plans at a meeting in September, the changes will begin in April in the UK and 2027 in Ireland. The list of branches which could close has not been decided.
The Samaritans, considered the fourth emergency service by its staff and volunteers, play a key role in suicide prevention, offering round the clock telephone support to people in distress.
Volunteers who answer the calls are based in offices around the country, many of which will now close.
The BBC has been told more than 50 branches, over a quarter of the total, have been raising concerns on an internal forum since the proposals were announced.
Plans for "virtual volunteering" where people answer calls from home, have sparked fears volunteers could leave the charity due to the pressures of dealing with calls about suicide alone.
Others only decided to help out due to feeling isolated at home.
Female volunteers have also said they would be uncomfortable with remote working due to the number of abusive and sexual calls the charity receives.
In her message to staff, Ms Bentley said some offices were failing to retain enough volunteers and "don't support the effective delivery of our services to callers".
She also expressed concern that too much of the Samaritans' income is spent on "maintaining bricks and mortars, rather than being used to improve our services".
But it is the loss of the intimacy and support the offices provide that worries many volunteers.
They fear the charity's proposals will create large, impersonal call-centres in big towns and cities, reducing the likelihood of people from rural areas being able to volunteer and undermining the meaning of being a Samaritans volunteer.
In its latest accounts, for 2023-24, almost two thirds (£15.3m) of the charity's £24.6m income was spent on staff costs and less than 4% on land and buildings.
"We're not against change," one volunteer told the BBC, "but they've not provided any evidence these changes will improve the charity. It feels more like the professionalisation of the Samaritans."
The proposals, if enacted, would also see the charity withdraw from some current activities, including talks in schools and providing the Veterans Emotional Support Line.
In a statement to BBC News, the Samaritans emphasised that their services would continue to be available every minute of every day, so people should always be able to contact them.
"Samaritans provides a life-saving service, day and night, 365 days a year but the changing needs of our callers and volunteers mean thinking differently about the way our services need to work," said Ms Bentley.
"We are engaging with our volunteers on proposed improvements that will mean we are able to answer more calls, have more volunteers on duty and be there for more people in their darkest moments.
"Samaritans volunteers are hugely dedicated to being there for our callers and they remain at the heart of our service, but it has become increasingly clear that having over 200 branches, varying in size from 10 to 300 volunteers, is not sustainable and hinders us providing the best possible service to people who need us," she added.