Barristers who handle criminal cases in England and Wales are beginning protest action over the amount they are paid to represent defendants.
Barristers say they are not paid enough for legal aid cases
The protest, which is likely to disrupt courts, stems from the freezing of legal aid rates in trials lasting up to 10 days since 1997.
Some barristers are expected to refuse to take new cases or appear in court.
The government has admitted the payment system needs reform, but said overall, defence barristers' pay had gone up.
The Department for Constitutional Affairs has said it accepts some junior barristers do have financial problems.
But ministers are awaiting the findings of a wide-ranging review before making any changes.
Barristers are self-employed and, by law, cannot go on an organised strike.
However, it is thought that many - particularly in the north of England, the Midlands and south Wales - will refuse to take on new work.
Hearings may be postponed and the action could cause serious disruption to courts if it continues.
The government's fixed pay rates, which are known as "graduated fees", were introduced eight years ago and apply to crown court trials lasting up to 10 days.
Hourly rates for the 95% of crown court trials which last up to 10 days have not changed since 1997.
The freezing of legal aid rates has amounted to a reduction of almost a quarter in real terms.
Further cuts, which take effect from Monday, mean that defence QCs and those in longer trials will also receive less money.
Current hourly rates for defending in legal aid cases are £33.50 for a junior, £47 for a leading junior and £62.50 for a QC.
Barristers want the rates to be kept in line with the rate of inflation at the very least.