Citizens Advice Scotland warned today that it was at "breaking point" after a £20 million cut to its budget and a surge in demand for help at benefit tribunals.
It has been barred from spending legal aid money on welfare cases, yet advisers represented people at more than 4,500 benefit tribunals last year - a 118 per cent rise since 2010.
It said many of the cases involved government decisions denying people employment support allowance and a 55 per cent rise in sickness benefit cases in the past five years.
That allowance helps those with disabilities or chronic illnesses.
But campaigners say that privateer Atos's "tick-box" testing is designed to cut the welfare bill at vulnerable people's expense.
Atos rejects that, but about 115,000 people have won appeals against its decisions, and a judicial review into the scheme opened today.
Citizens Advice Scotland chief executive Margaret Lynch said her staff had seen the fallout from cuts "first-hand and it is set to get very much worse.
"We are already at breaking point so we desperately need to be adequately resourced to enable us to help those who need it most as we aim to mitigate the impact of welfare reform as much as possible," she said.
A Department for Work and Pensions spokeswoman claimed that the cuts had made the welfare system fairer.