At least five principals have now quit their posts since OFSTED took over the inspection of further education colleges in April last year.
Peter Pendle, general secretary of the Association for College Management, said principals are too often "the scapegoats" when a college is criticised by OFSTED.
The ACM is now backing plans to set up a leadership and management college to provide college leaders with the required skills.
Ian Bentley resigned "for personal reasons" as head of South Devon College in Torquay after the inspectors called.
Principal casualties, 36