An Onchan MHK breached conduct standards and must apologise to Tynwald, a report has found.
Author Mark Egan concluded Mr Callister broke rules when he told staff “if I am going to the gallows over this, I will take my friends with me”.
Mr Callister refutes the findings and described them as “deeply upsetting”.
Mr Egan was called by the Tynwald Standards and Members’ Interests Committee to carry out an independent investigation in December.
Mr Callister alleged he was subjected to “aggressive questioning” which amounted to bullying by departmental members Joney Faragher, Michelle Haywood and Tanya August-Hanson.
They denied the allegation and civil servants told Mr Egan they had not seen inappropriate behaviour by the members towards Mr Callister.
Mr Egan therefore found conduct standards had not been breached on this occasion.
‘Going to the gallows’
Meanwhile, the investigation heard claims that during his time as health minister Mr Callister said to staff in his department: “If I am going to the gallows over this, I will take my friends with me.”
Mr Egan felt the comments could be interpreted as implying staff would suffer consequences as a result of a decision which could put Mr Callister into political difficulty.
He therefore found Mr Callister had breached Tynwald standards of conduct.
The report also found Mr Callister broke rules when he told a civil servant all of the political members in the health department wished for the individual to “consider their position”.
In an open letter online, Mr Callister denied ever saying this and said it was “deeply upsetting” Mr Egan had found him not to have “acted in a manner consistent with the principle of honesty”.
The investigation was also told Dr Haywood had sworn at Mr Callister during a heated discussion after he had referred to her in a disrespectful manner.
After Mr Egan’s research he concluded that Dr Haywood had not breached standards.
Mr Callister’s apology is expected to be made at next month’s sitting of Tynwald court.
The cost of the investigation was £3,000.