The volunteers first walked out after an unnamed volunteer was asked not to return because of allegations against him of bullying (2 July, page 3).
A panel set up to consider the sacking - consisting of a person independent of the CAB and a board member not previously involved in the dispute - upheld the decision.
The volunteers, who have clocked up a combined total of more than 250 years' service at the bureau, said the process had been "flawed and unfair" and claimed their colleague not been given enough information about his alleged offence.
The group claims the bureau has been left with only three volunteer advisers. Bureau chair Liz Levett said this was not true but was unable to say exactly how many remained.
Levett said she regretted the volunteers' decision but said the person concerned had been given sufficient information to mount a defence.