While Carnival does say that you can remove the autotip with the purser once you are on board, in my experience it was impossible to do. During a Carnival cruise in August 2006, I went multiple times to the purser during the voyage to request removal of the autotip feature from my account. I was rebuffed each time with the excuse that 'the computers are down and they could not communicate with company HQ in order to remove the autotip.' The purser claimed that they could not remove the autotip from my account locally.
Somehow, I find it hard to believe that company HQ would be out of communication with one of their vessels for several days. I finally gave up trying. I would like to comment that, in all the emails on this subject, no one seems to be holding the cruise line responsible for ensuring that their employees are adequately compensated for their labors. I, as a passenger should not be in the position of ensuring someone's wage. I do not feel that I would be stiffing the crew if I did not pay the autotip. A tip is not a wage but, rather, it is something a little extra that is freely given to whoever should be rewarded for going aboe and beyond.