Existing joing condition change suddenly

Sir/Ma'am When I was join organization there was a three months notice period from both sides it will be pay on basic salary and I was working here last 6 years but two months ago all employee received a email having one attachment with A 4 signed paper if someone left job before notice period it will be paid on gross salary i.e company deducted amount on gross salary and pay leave(EL ) and other on basic salary to employee after changing this condition my total loss around 80 thousands And I want to join another organization if I am protest against this and show the policy they warned to me if next company call us for verification your feed back may be not good Please suggest to me how I can handle this situation