The Legal Services Commission, which operates the legal aid scheme, is cutting the mileage rate for cars from 45p a mile to 25p and urging lawyers to use public transport.
The move is part of Government attempts to slash £350?million from the annual £2?billion legal aid bill.
Lawyers say they were not notified to the changes to the travel expenses system and that carrying confidential files on public transport is impractical.
But many lawyers warn it is impractical and dangerous to catch buses while carrying confidential documents.
Now lawyers are to make submissions to the Legal Services Commission to get the mileage rates resorted.
Charlotte Riley, crown court department manager at Staffordshire law firm Beswicks where 95 per cent of work is legally aided, said: 'We had no notification of these changes.
'The first we knew about it was when claim forms started coming back, saying the LSC would only pay 25 pence per mile.
'Most of the lawyers are out at court every day, so all these claims add up.'
She said: 'The mileage rate has been 45 pence a mile for around 15 years - but now, we are being told we have to justify why we haven?t used public transport.
'Carrying all our confidential files to the bus station and then getting on a bus is not practical.
'I haven?t got anything against public transport but we would end up getting on a bus with clients who would want to discuss cases and, in some cases, it could cost more than paying petrol.
'It also wouldn?t go down very well if we were late for court because of delays on buses. And most of the prisons we visit are in the middle of nowhere.'
Stuart Muldoon, from Stevens Solicitors, said: 'Our costs have been reduced automatically without any further consideration.
'The LSC isn?t taking into account the distance we have to travel, or where the court or prison is in relation to public transport routes.
'It can take a lot longer to get to places using public transport but this does not seem to have been taken into consideration.
'We are appealing, but all we get is a note back on our claims saying we should use public transport.'
The LSC which runs the legal aid network in England and Wales said: 'The approach to assessing mileage claims has been established for many years, and we outlined the payment rates in 2011 and again in May 2012.
'Legal aid is public money, and where public transport can easily be used to get a solicitor to court, it is only fair to the taxpayer to pay the appropriate amount from the public purse.'