Gee I see no one has posted an answer to your guestion... I don't own a jet table saw and really don't know what the fence looks like but if the fence is moving that much something has to be wrong... could you give us a few more details like when does it move? Does it stay parallel to the blade? Does it have a locking method.... well you get the idea the more information we have the better someone can provide some ideas as to what is wrong (model numbers etc also help).
Ed
Ed