At every official Tournament is a Head Judge. This is the most important person at every tournament, the one that hands down official rulings as necessary. This person also gives out and takes record of all warnings for each participant, and once a player has crossed the line they can expect the Head Judge to remove them from the tournament.
At low-level tournaments, such as locals, you can expect to only have a Head Judge present. But at higher level tournaments, such as Regionals, there will be many Judges present. In this case the Head Judge will likely remain with the Tournament Organizer to make sure the tournament is running smoothly until he is called by another Judge to give a final ruling.
While you can appeal a Judge's ruling to the Head Judge, the Head Judge's word is final. Once a Head Judge's ruling has been given, you must accept it and continue play following his instructions.