Bernstein's decision, which follows last week's resignation of managing director Chris Bird, stems from about an apparent difference of opinion over transfers and financial issues within the City boardroom.
In a statement, the departing Bernstein said: "Over the last few months, there has been a divergence of views on fundamental strategic issues, particularly concerning finance and management structure.
"I believe this has inhibited my ability to direct the club in the way I would wish. On my appointment in 1998, I emphasised three factors required to fulfil the chairman's role effectively - unity, stability and professionalism.
"Until recently, my board, major shareholders and key employees have successfully worked together to achieve these."
