The appeal to the New Zealand Supreme Court involves a ruling on evidence and represents one strand of the complex legal case against executives from the file-sharing site.
U.S. prosecutors shut down Megaupload last year, accusing the executives of racketeering by facilitating massive copyright fraud. Dotcom says he's innocent and can't be held responsible for those who chose to use the site to illegally download songs or movies.
Dotcom and his colleagues had sought access to all the U.S. evidence against them. A lower court ruled in their favor, but an appeals court overturned that ruling, saying extensive disclosure at the extradition stage would bog down the process and that a summary of the U.S. case would suffice.
The extradition hearing against the four men has been postponed once, from March to August, due to legal wrangling and now may now be postponed further. Dotcom and the others remain free on bail pending the hearing.