Natfhe, the lecturers' union, claims there has been a particular problem in one department, English for speakers of other languages (ESOL) where, it says, almost 40 staff have left in the past two years.
The college management disputes the number. It says it has looked into reasons for the departures and that none relate to bullying. "It is a grade 1 department," said vice-principal Marie Gilluley. "There is a high turnover of ESOL staff in every college."
There is also tension in the trade union education department, from where two staff were made redundant at the weekend. Natfhe, which has taken up their case, claims long-standing staff are being victimised for union activity.
Mancat lecturers were among an estimated 80 taking part in the demonstration calling for dignity at work.
But Ms Gilluley dismissed the event, saying that only six of its lecturers were involved. Natfhe insists that almost half the demonstrators were past and present lecturers.
One Natfhe activist claims to have been called a "middle-class tosser" by principal Peter Tavernor - something the college has not denied. "I believe it was said but that was a year ago," the spokeswoman said.
Mancat says that trade union education is just one area identified as being potentially overstaffed.
Management rejected Natfhe's offer to save jobs by having five lecturers work an 80 per cent timetable.
The college said this would create "real difficulties in deploying staff to cover the likely pattern of work".
Colin Gledhill, north west regional officer for Natfhe, described Mancat as "unique in the North-west for the ferocity with which it reacts to people who oppose it.
"We have either won or settled at the door in almost every case.
"I believe the number of cases raised by members against Mancat, either through the union or privately has been disproportionate.
Barry Lovejoy, head of Natfhe's colleges department, said: "Bullying accounts for a large proportion of the cases we take up. It is linked to starvation of funds and managers and principals under pressure from the system.
"The issue of bullying in general has plagued our sector and continues to do so."
Ms Gilluley said:"Our recent LSC provider performance review reports that there is strong management and leadership in the college. We have a highly satisfied workforce and no evidence has ever been produced to substantiate any claim of bullying."