Campbell Pearson decided to take the Educational Institute of Scotland to court after the EIS presented a dossier to the Scottish Office. The Scottish Office then conducted "a lengthy and thorough examination" last year before eventually clearing the college of the most serious charges.
A hearing has already been held at the Court of Session in Edinburgh before Lord Cameron of Lochbroom whose ruling is expected shortly.
The latest chapter in the history of troubled relations between the college and the union stems from allegations, including "intimidation", "dishonesty" and "misuse of college money", made by EIS members at the college more than two years ago. A staff vote of no confidence had been passed in the college management in September 1994.
Mr Pearson believes he was defamed in the dossier passed by the EIS College Lecturers' Association to the Scottish Office in December 1994.
The union says it successfully argued "qualified privilege", under which it says it had a duty to reveal the information to the Scottish Office.
Mr Pearson raised his action under the Administration of Justice (Scotland) Act 1972,. If he wins, this would force the EIS to reveal the names of its members at Borders College who had raised their concerns with the union nationally. The institute has refused to identify its "moles" in order to preserve its ability to represent its members and out of fear that Mr Pearson would take legal action for damages against them.
Mr Pearson said this week that the matter was a personal one and he had no comment to make.
The internal affairs of the college are due for another public airing next February when an industrial tribunal resumes hearing claims of unfair dismissal brought by two former members of staff, one of them the EIS branch secretary at the college.
A previous tribunal last year awarded record damages of Pounds 11,000 to a sacked lecturer whose redundancy was ruled to be "manifestly unfair".