Proposed reforms to legal aid in England and Wales are threatening an "incredibly fragile" system, the Law Society has warned.
The solicitors' body told BBC Radio's Five Live Report that hundreds are deciding to end legal aid work.
The proposals will see lawyers bid competitively for all legal aid work instead of working for set hourly fees.
Lord Carter of Coles, who put forward the reforms, says they will improve legal aid provision across the country.
A consultation exercise is under way.
The Citizen's Advice Bureau opposes the reforms.
It has warned that tight budgets and a shortage of lawyers under the current system have led to parts of England and Wales becoming "advice deserts" for those eligible to receive advice funded by legal aid.
Martin Lord, bureau manager at Northampton district Citizens Advice Bureau, said: "It's not uncommon to have to refer clients all the way to places like Leicester or Peterborough [for legal advice]."
The government's reforms are designed to tackle this but carry a 5% cut in the ?2bn annual budget.
Labour has a long-standing commitment to reducing the cost of legal aid.
June Venters, who recently became the first woman solicitor QC, says Lord Carter's proposals will mean that she will be forced to quit legal aid work for more lucrative private work.
"There comes a point when, if I go below a certain level of payment, I'm no longer in business. And that is what these proposals will result in."
Lord Carter, who accepts there are some "advice deserts", says his reforms, aimed at implementing a sustainable market-based procurement system, are the most effective way of tackling the problem.
This market will be driven by competition based on quality, capacity and price, he said.
"I'm suggesting marketisation of legal aid. One of the consequences of that, we hope, is that prices will rise in areas where there are deserts to attract [solicitors] in, just as we think in over-supply areas they'll go down."
Also proposed by Lord Carter is a wholesale move towards larger solicitors firms.
He suggests, through efficiencies in scale and increased volumes of work, these firms will find a more rewarding and sustainable return on lower fees.
The Law Society estimates as many as 800 law practices may close as a result of Lord Carter's proposals - equivalent to a quarter of all current providers of legal aid advice.
Desmond Hudson, Law Society chief executive, said: "What we are seeing is a supply base of legal aid solicitors that is incredibly fragile and at extreme risk."
Over half of the ?2bn budget is spent on criminal legal aid.
By contrast, spending on civil legal aid has fallen in real terms by 24% since 1997, which critics say leaves thousands of people without access to justice.
Conservative MP and shadow solicitor general Jonathan Djanogly said he was extremely worried about the provision of legal aid.
"We're talking about very vulnerable individuals being at risk because the number of solicitors is declining, so people aren't being represented."
He also expressed concern about Lord Carter's proposal on restructuring the system.
"What we do have in this country is a high street system, a local system, where people know they have access to solicitors who they know and who understand the community.
"What we are talking about here is that structure being destroyed. A year ago I had concerns for the system. Now I would say it's a meltdown."