Analysis: Although the tension and personal bitterness within the ASTI has been known to the general public for some time, Mr Lennon's affidavit exposes it in a vivid and graphic way.
Mr Lennon describes how he has been under great stress and how he has been suffering from vertigo as what he sees as the campaign waged against him takes its toll.
Mr Lennon says there have been tensions in the ASTI since former president Ms Bernadine O'Sullivan took the union out of the ICTU and made a claim for a 30 per cent pay increase in 2000.
During the last few years, Mr Lennon says he has been subject to a persistent pattern of abuse and harassment. People have sought to undermine him because it is suggested he was not whole-heartedly committed to the union campaign for a pay rise. He says in the affidavit: "I have continually rejected that broad criticism which has no foundation."
He says the campaign against him takes the form of abusive comment, interruptions, gratuitously offensive comments, lies, barracking, repeated exaggerations, innuendo and snide comments.
His essential point, in a very lengthy affidavit, is that the complaint of bogus expense claims made against him by the union treasurer, Ms Patricia Wroe, is an old complaint which she has revived because she believes the current inquiry team will find against him.
His other key point is that this inquiry team - ASTI president Mr Pat Cahill and vice-president Ms Susie Hall - are biased against him. Both, he says, are ill-disposed towards him and have displayed prejudice against him in the past.
He is particularly critical of Mr Cahill with whom, he says, he has had strained relations since the early 1990s. According to Mr Lennon, in his affidavit: "Since that time he (Mr Cahill) has engaged in several bouts of bizarre and abusive correspondence with me, making all sorts of denigrating and unfounded allegations against me." Mr Lennon also says that Mr Cahill, when canvassing for votes for the vice-presidency of the union in 2002, told an executive member "that it was his intention if elected to try to achieve my dismissal as general secretary".
Mr Lennon says in his affidavit that Ms Wroe is a "person who has displayed clear bias, ill will and prejudice against me in the past".
Mr Lennon says he is quite willing to allow any fair-minded group investigate her complaint but not the current inquiry team which is prejudiced against him.
If the existing investigation is allowed to proceed, it will, he says, inevitably lead to disciplinary action and possibly even "deprive me of my livelihood".
Mr Lennon says the specific allegation of bias made against Mr Cahill and Ms Wroe have not been addressed by them "save by way of general counter-assertion".
Mr Cahill has said the ASTI will vigorously contest Mr Lennon's statement at the next court hearing on October 6th. He has also told The Irish Times that he has at all times acted in an independent and unbiased way.