B Clam, that is not acceptable, and would be unenforceable (probably in law).
There is a precedent for a reducing bond but your company, or any other company, are applying an unfair restriction that would give them little or no chance of winning an action for the whole amount while you have "worked off" a major part of the bond. That is how it was setup in the first place.
You should request a review of your contract with your company as soon as possible, and should ask that it be adjusted.
Then take it from there.