Carpetbagger.com website co-ordinator Richard Yendall is calling on Portman Building Society members to support a campaign he says will defend their rights.
He wants 500 members to sign a resolution aiming to lay down strict guidelines on expulsion of members.
The new resolution is aimed at preventing the society from expelling or threatening to expel a member for proposing a resolution or a candidate for director.
Yendall also wants existing directors to sign away to charity, any future windfall benefits arising from a demutualisation.
Yendall was one of 500 members expelled from Portman earlier this year for signing a demutualisation resolution.