The dissident Motor Trade Finances shareholders say the company's defensive reaction to requests for information has left them more worried.
They have written to fellow shareholders about their concerns, ahead of the special meeting they called to take place next week.
Relying on comment by Michael Warrington at the investment advisory firm, Chris Lee & Partners, the shareholders say a liability could be up to $30 million, plus interest.
That's what MTF earned in fees in the three years prior to last year's High Court judgement, which ruled that some of the fees MTF charged were unreasonable.
MTF is appealing that judgement, and has already spent half a million dollars on legal fees in 2012 and another million dollars in 2013.
Mr Warrington's interest in MTF follows Heartland New Zealand's interest in possibly buying MTF.
But Heartland says it can't begin to put a price on MTF because of the legal situation.
Mr Warrington said the court case made it clear that Heartland's concerns were valid, though he noted that the case had been appealed.
He said the judge had relied on expert opinion from an accounting professor over appropriate fees being best related to the variable costs of a loan, rather than the fixed costs of a business.
"The court found that MTF had allocated almost all of their expenses or overheads to fees," he said.
"The judgement made it reasonably clear that the fees were excessive, and therefore some would have to be returned".