A no-deal Brexit would cause charities to collapse and leave a vacuum of support that could not be filled, the Scottish Council for Voluntary Organisations has warned.
Anna Fowlie, the chief executive of the umbrella body, has written to Boris Johnson, the Prime Minister, calling on him to "end the calamitous drive towards a no-deal Brexit".
In the letter, sent yesterday, Fowlie says that, despite being largely opposed to Brexit, the sector in Scotland had hoped the issues it raised would be discussed in a "serious and responsible way".
Instead, the sector’s voice has been "drowned out", she writes.
"Having tried to communicate with government on everything from human rights, environmental impact, immigration, free movement and workforce to medicines, loss of funding and maintaining links with sister organisations, we have merely been invited to a series of unhelpful and uninformative meetings," she says in the letter.
"This situation is no longer tolerable."
She describes a no-deal Brexit as a "reckless act" that is "set to take place without proper consultation and deliberation" and says it should not be allowed to happen by default.
"It is clear a perfect storm is brewing for voluntary organisations and the people they work with," the letter says.
"Increased demand for assistance, coupled with a loss of funding, staff and volunteers, will undoubtedly see charities collapse and leave a vacuum of support that cannot be filled."
Fowlie warns that a no-deal Brexit would make it "impossible" to maintain the existing levels and standards of support.
"It is time to end the calamitous drive towards a no-deal Brexit, which will wreck communities, lives and organisations that so many people rely upon," she says.
She finishes by calling on Johnson and the leaders of other political parties, who were copied into the letter, to stop the UK exiting the European Union without a deal.