Nearly 600 council workers in Lanarkshire have joined a planned action against their unions over "bad advice" during the equal pay dispute.
Members from Unison, GMB and Unite have signed up to the claim that they were misled or poorly represented during the dispute at North and South Lanarkshire councils.
The group allege:
Unison and GMB say they will "vigorously" defend any action, while Unite declined to comment.
The issue centres on advice given during the initial wave of equal pay claims against both councils in 2005.
Members claim they were urged by unions not to join an independent action run by solicitors Stefan Cross and Carol Fox.
The allegations hinge on evidence provided by former union representatives.
Former Unison steward John McLaughlin - a care worker at South Lanarkshire Council - is taking part in the action.
He told STV News that he passed on "bum advice" provided to him by union officials.
"See nearly every one of [the members], I sold them a pup," he said.
"I told a whole rake of them there is absolutely no claim. I was standing there in my shirt and tie, representing Unison, telling them there is absolutely no claim.
"I don't know if you've spoken to all 500 of these people, but I'll tell you right now - if any of them are from South Lanarkshire Unison, there won't be a lot of them giving me a good name.
"I got a really bad name because I let them all down. Simple as that."
Breaking down, he continued: "I was only telling them what I was told to tell them for years.
"It's not about the money. It's about the lies people have been telling from day one, trying not to give them their pay."
Some of those advised by John are also involved in the planned action, which is run by claims firm DM Legal.
Elaine O'Donnell, a care worker in South Lanarkshire, said: "I know two people who got three-and-a-half times as much as I got. They started the same day as me, were on the same hours as me, and I think it is very wrong."
Retired carer Patricia Brown also claims she was warned equal pay settlements would result in jobs losses.
"They [Unison] never done anything to help us," she said. "This was a quick fix."
Her colleague Lesley Millar states her union, Unison, were "negligent" in handling her case.
"It's like they wanted to shut it down as quickly as possible - and I want to know why."
DM Legal - based in Wishaw - is operated by two claims advisors who are instructing an advocate to litigate on their behalf.
The company claim they are in talks with the unions in a bid to settle for many of their clients.
But Stefan Cross QC - a veteran equal pay campaigner who has taken on councils and unions across the UK - said the case will be "difficult" to win.
"The problem is working out who said what to whom and when," he added.
Because DM Legal can't litigate on their own, union sources described the action as an attempt at a "shakedown".
Earlier this year, GMB commenced court proceedings against its former legal advisers, Digby Brown, "in relation to advice given on equal pay claims".
But the union said: "We are well aware that a firm called DM Legal Claims Limited, has been making allegations publicly against our union for a number of years now.
"Should DM Legal Claims Limited ever actually provide particulars for their allegations and move to legal proceedings, then rest assured that we would defend our trade union vigorously."
A Unison spokesman said: "There are no legal claims against Unison from members in North Lanarkshire Council or South Lanarkshire Council.
"Unison strongly refute any claims of wrongdoing and will vigorously defend any action against us, should any be forthcoming."
Unite and both councils declined to comment.
There are currently 27,000 outstanding equal pay claims in Scotland, according to a report last year.
Settlements have so far cost £750m - with nearly a third of that total attributed to North and South Lanarkshire Council.