"Staff who got on the wrong side of her had their lives made hell."
Hugh McGinley, who worked for MJM International for six years before resigning, claiming pressure and stress, gave evidence for a second day at a tribunal in Glasgow.
He said: "In my six years there if staff had a dispute or got on the wrong side of Michelle their lives would be made hell."
Mr McGinley is claiming £20,000 compensation for constructive dismissal.
He looked visibly upset when he told of finding out that a listening device had been discovered last year in the office of Scott Kilday, the firm's operations manager.
He said he was in Mr Kilday's office up to 20 times day discussing business and personal family matters.
When asked how he felt when he realised his private conversations were being listened to, he said: "it just sickens me."
Mr McGinley said he reported the bugging incident to police and was told it was not a criminal matter.
The tribunal continues next week.