Family lawyers have reduced the number of legal aid cases they have taken on by more than 50%, a poll has shown.
Family lawyers said they could not afford to take on legal aid cases
The Family Law Association (FLA) said its members supported the Bar Associations' dispute.
The Scottish Executive has been accused of failing to increase legal aid fees in line with court reforms.
The FLA, which is petitioning the executive, warned that low income vulnerable families would be the hardest hit.
The row centres on delays in the introduction of a new system of "block" fees, and an executive offer of an interim increase in fees under the present system.
The executive said it was committed to setting rates of payments which ensured fair remuneration.
Helen Hughes, vice-chair of the Family Law Association, which represents more than 300 family lawyers across Scotland, said she was supportive of the stand taken by the Bar Associations.
"As with criminal cases, family cases are rarely simple and often very high maintenance involving issues such as domestic violence and substance abuse," she said.
"With block fees it doesn't matter if you have one meeting or 100 with a client, the fee is the same amount."
She said the system could work but needed to be flexible.
"It makes no allowance for complex cases that can require a great deal of preparation and court time," she said.
"Our member firms are finding that they simply cannot afford to take on legal aid cases and that ones that do are overloaded with cases and can't help everybody that needs it.
"There is also a knock-on effect of a shortage of lawyers to take on family and criminal legal aid cases as commercial practice is far better paid."
She added that lawyers throughout Scotland were hopeful that a settlement could be reached before the August deadline.
Bar Associations in Glasgow, Edinburgh, Hamilton and Dumbarton are to withdraw their representation of alleged sex offenders over the delay in introducing the new payment structure.
There has been no increase in criminal legal aid fees since 1992 and an interim pay offer has been declared unacceptably low.
Block payment fees were introduced for civil cases in October 2003.