The cities' bar associations have written to the society questioning its decision to accept revised Scottish Government proposals on legal aid in the face of opposition from its members.
It comes as hundreds of lawyers are expected to demonstrate outside the Scottish Parliament today.
The changes would see accused people with a weekly disposable income of more than £82 forced to pay a contribution towards their legal aid.
The defence solicitors claim the move, being introduced under the Scottish Civil Justice Council and Criminal Legal Assistance Bill, will result in miscarriages of justice as people choose to represent themselves in court or plead guilty to avoid the costs.
They are also unhappy at being asked to collect the contributions from clients and believe the Scottish Legal Aid Board (Slab) is better placed to do so.
Mark Harrower, of the Edinburgh Bar Association (EBA), said: "There's growing interest in the protest – not just in relation to the Bill but to other aspects of the justice system the Government plans to change.
"We worry for the stewardship of our justice system under the SNP Government and a justice minister who has shouted us down and talked over us.
"We're going to send a message to the Government that they may have decided what is happening, but we aren't giving up."
Lawyers' associations have staged a number of protests at the plans, which will be up for a final debate today in Parliament.
The law society, the Government and Slab came up with a series of amendments to be considered – the main one being the contribution threshold be increased from £68 to £82 – but a majority of society members rejected them. Despite this, the society agreed the amendments.
Mr Harrower said the association had written to the Law Society of Scotland president, Austin Lafferty.
He added: "The profession has now had to take a step back and reassess its relationship with the society. It may be that its Legal Aid Negotiating Team (Lant) is not negotiating in our best interests and we're now going to have to stand up for ourselves.
"Should the Bill be passed, which I'm sure it will, there will be further protest action and the start of a new attitude because we really can't rely on the society to fight our corner – we need to do it ourselves."
In a letter to the society, Ann Ritchie, president of the Glasgow Bar Association (GBA), said questions about the Lant must be answered "in order that those practising criminal defence work can decide whether they are happy with the representation provided by the Lant and, if not, whether attempts should be made to engage with the Government independently".
Mr Lafferty said: "We are open to having a full and frank discussion with the EBA and GBA and indeed any of the faculties that wish to discuss the role and remit of the Lant.
"The society remains opposed to the principle of collections.
"I absolutely believe that without the Lant there would have been no progress made on the level at which accused persons have to make a contribution, which now comes with a guarantee that such a change won't be paid for through cuts to solicitor fees, or any shift on solicitors having to collect from prisoners on remand or custody."
"Our fear was what would have happened if the package had not been agreed. No improvements would be in place, but the original collections regime would have proceeded.
"This is not the Bill we would have wanted and there is no doubt we will have to revisit these issues in future."