Solicitors have said they could become unpaid debt collectors as a result of proposed legislation aimed at making more people contribute towards their criminal legal aid.
Scottish Government proposals, if passed, will mean people who have disposable income of £68 a week must make a financial contribution towards their legal bills.
The Law Society of Scotland has said the plans are unfair and it also objects to solicitors having to collect the contributions themselves.
Oliver Adair, convener of the society's legal negotiation team, said the legislation would leave them as unpaid debt collectors and insisted that the Scottish Legal Aid Board should be the "obvious body" for collecting such money.
The Scottish Government has published draft legislation with the stated aim of saving £3.9m from the legal aid budget.
Anyone with disposable income under £8 a week would pay nothing towards the cost of legal aid, according to the Scottish Civil Justice and Criminal Legal Assistance Bill.
A contribution would be paid if disposable income is above £68 but under £222 a week. Above the upper limit, assistance will only be given if the board considers that contributing money would still cause "undue hardship".
The Scottish Government has said about 80% of people receiving legal aid would continue to pay nothing and that the Bill would end a situation where contributions are collected for civil cases but not for criminal cases.
Justice Secretary Kenny MacAskill has said that it is "right and proper that those who can afford to pay towards the cost of their legal defence costs do so".
Mr Adair said the society agrees that those who can afford to contribute should do so, but said: "The Bill proposes that the threshold for determining whether a contribution is payable should be £68 disposable income a week. We do not believe that is a realistic amount from which to expect anybody to pay towards their legal costs.
"We also have concerns around some of the areas which would be included in disposable income calculations, such as disability living allowance and war pensions. This would mean some of the most vulnerable people who rely on legal aid could have to pay a sizeable contribution towards the cost of their defence directly from their benefit payments.
"The Bill as its stands would leave solicitors as unpaid public debt collectors. The Scottish Legal Aid Board is the obvious body for collecting the contributions. After all, they already collect contributions in civil legal aid cases and have procedures in place to carry out large-scale collection of contributions."
The Bill also aims to establish a civil justice council to replace both the Court of Session Rules Council and Sheriff Court Rules Council. The new body would have a policy role to advise and make recommendations on improving the civil justice system.
Kim Leslie, convener of the society's civil justice committee, said it backs the idea of having one overarching civil justice council. But it has serious concerns about the proposals to have just two solicitor-members on the new body, arguing that it should have at least six.
A Scottish Government spokesman said: "This Government takes access to justice very seriously. The criminal legal assistance element of the Scottish Civil Justice Council and Criminal Legal Assistance Bill will require that people facing criminal charges should pay a contribution to the costs of their defence where they can afford it. This will bring criminal legal aid into line with civil legal aid.
"More than 80% of applicants such as those on very low income or on benefits such as income support are still likely to be eligible for criminal legal aid with no contribution due.
"We have engaged constructively with the Law Society of Scotland on this issue and will continue to do so. We remain committed to taking on board constructive suggestions as the Bill progresses though the parliamentary process."