Torquil Montague-Johnstone, who stepped down as finance director last week, said he had not been shown a trading update which reassured investors that the company's performance was on track before it was issued to the Stock Exchange on 13 August.
Mr Montague-Johnstone says he wrote to Peter Kane, the chief executive, the following day dissociating himself from the statement.
Last week, Business Post shocked the market with a warning that earlier assumptions about sales were "unrealistic". Its shares almost halved in value and SBC Warburg, the house broker, reduced its full-year profit forecast to pounds 19.8m from pounds 22.8m.
Mr Montague-Johnstone believes Business Post has unfairly blamed him for misleading the market about the company's performance, and is demanding an apology.
He has also accused the company of "deficiencies" in its corporate governance. "Unless the company comes up with a retraction and an apology this could run and run," he added.
A spokesman for Business Post declined to comment.
The dispute centres on Business Post's board meeting on 12 August when Peter Kane, previously a non-executive director, was reappointed chief executive. His brother Michael Kane also took on executive responsibilities.
Mr Montague-Johnstone, who opposed the move, agreed to leave the group after working six months' notice. However, he says he did not expect the company to issue a trading update when it announced the changes to the Stock Exchange the following day.