Courts in England and Wales are expected to be affected by a two-day work-to-rule by angry criminal law solicitors this week as opposition mounts to government plans to change the way legal aid services are paid for.

The government could also face a high court challenge by the Law Society, the solicitors' professional body, which is taking legal advice about the prospects of a judicial review.

Lawyers said the proposals, which stem from a government commissioned review of the legal aid system by Lord Carter of Coles, would accelerate the flight of lawyers from legal aid work. The age profile of those doing criminal legal aid shows most are in their late 40s and 50s and few younger solicitors are attracted into a field that pays poorly compared with other legal work.

Ian Kelcey, the chairman of the Criminal Law Solicitors' Association, said the new contract offered by the Legal Services Commission, which runs the legal aid scheme, represented a minimum reduction of 10% in pay overall.

"That is against a background of 12 years of no increase in rates, costs rising over the same time by 50% and staff working harder and longer hours just to maintain the status quo," he said. By contrast the Crown Prosecution Service had seen an increase in funding of about 40% over the last six years, he said.

Under the plans, solicitors will be paid a fixed fee for handling a case but Mr Kelcey, who is a solicitor in Bristol, said they had no way of predicting the number of hearings it would take or how far they would have to travel to see a client, who might be sent to a distant prison because local jails were full.

Payments for travelling and waiting time would be axed for urban practices but not for rural ones.

In a current drugs case, he said, he had two wasted hearings because of prosecution delays in producing the case papers. "Under Carter's proposals we would have one fixed fee for dealing with this work irrespective of the efficiency of the prosecution agencies, the court, and the police service when it comes to interviews at police stations," he said.

Robert Brown, executive officer of the London Criminal Courts Solicitors' Association, said the Carter proposals hinged on large volumes of work for solicitors.

But that had changed since a means test introduced in October had led to a 29% drop in the numbers qualifying for legal aid.

The Department for Constitutional Affairs said: "Disrupting the criminal justice system and harming the interests of victims, defendants and the court system is unnecessary and irresponsible. Whilst some delays may occur in some courts, staff in the criminal justice agencies are working very hard to keep this to a minimum."