Hugh McGinley, 52, is suing Miss Mone's company MJM International for constructive dismissal and is asking for £20,000 compensation for loss of earnings.
Mr McGinley claims his workload increased substantially after his immediate boss, the finance director, left and was not replaced.
He told a tribunal in Glasgow that he was forced out of the job he had held at the company for six years because of stress and pressure.
Mr McGinley said the demands made on him by Miss Mone increased at the end of 2012, when the company was in "serious financial difficulties".
Mr McGinley told employment judge Jane Garvie that previously he had had very little to do with Miss Mone.
But he said that after the financial troubles began - when a takeover was being considered -the emails he received from her increased from eight over a 10-month period to more than 400 in just four months.
The accountant, who earned £37,000 a year with the company, said that most of the correspondence related to the financial situation, but added that some were in his opinion trivial.
He said: "One email from Michelle Mone on January 21, 2013, was a request for the Costco membership to be renewed. Previously there had been six employees on the card. She said the only people to be on it were to be her and her mother Isobel.
"This took me away from my time and efforts to produce information in a timely manner during the takeover."
Mr McGinley added: "Every request from Michelle was urgent."
He also said he was caught in the middle of the acrimonious break-up of the marriage of Miss Mone, who was director of MJM, and her husband Michael Mone, the managing director.
This culminated in Mr Mone leaving MJM, which is now known as Ultimo Brands International, on February 6, 2013.
Mr McGinley told the tribunal that Mr Mone was his line manager.
But he added: "She [Miss Mone] made it clear she didn't want the financial situation discussed with Michael. She also asked me for information I had given Michael. I was just caught in the middle."
The accountant left the company on March 1 last year, just after Miss Mone and her husband Michael had parted company both personally and as business partners.
They had started the lingerie company from scratch, but after their separation, Michael Mone set up his own underwear company.
The tribunal had previously heard that some of Mr McGinley's conversations were bugged because it was feared he was betraying company secrets.
The tribunal continues.