Judges are considering legal action to block an increase in their pension contributions.

The judges claim that the changes, which follow the 2010 Hutton report on public service pensions and come into force in April, would be unlawful and have set up an action group to fight them.

The lord chief justice, Lord Judge, has written to all members of the judiciary telling them about the potential challenge. Magic circle firm Clifford Chance would not comment on a report in The Times news­paper that it had been approached to obtain quotes for legal advice.

Judges’ salaries range from £103,000 to £240,000, less than many would receive by remaining in private practice. The pension package is touted as one of the factors that encourages judges to make the move.

At present salaried judges make no personal contribution to pensions which are among the most generous in the public sector.

The deal was negotiated by the former lord chancellor, Lord Falconer, on the grounds that judges are a special case because of their constitutional independence.

The change would require them to pay 1.28%. A spokesman for the judiciary said talks are ongoing.