You have to prove that the additional cost will be a hardship to you (I don't remember the exact legal terms). Some people have had success getting out of their contracts with these kinds of changes, but usually it does not work. Like MissJennell said, they can simply issue you a credit to take care of that. I don't remember what the fee is now, but even if it went from 0 to 1.50, they can issue a $36 credit to offset that change.
If you want out of your contract, you can try and use this point, and if you talk with the right person, you might succeed, but I wouldn't think it would work for very many people.