Nope, if you're registered. If you aren't and it's only hearsay, next of kin word may override yours, as the doctors wouldn't really know your intentions and there wouldn't be any way to tell. So next of kin orders would be followed.
If your have a state recognized notarized health directive to 'pull the plug', doctors will pull the plug against any other next of kin's wishes. However, family can delay the process by going to court which, in case of organ donation, is really a bad thing.
If you do not make your wishes known in writing, you are leaving it to your family because what you wanted will be here-say. If it's their word against yours, they win because you are dead and no one will be able to verify what you wanted.
This is why it is SO important to have an advanced directive written up.