Internet mogul Kim Dotcom said on Monday he was offering a $5 million "bounty" to whistleblowers for information to help fight an online piracy case brought by the United States.

The Megaupload founder, who is resisting extradition from New Zealand, said he had to resort to offering the money because the deck was stacked against him in one of the largest copyright infringement cases ever brought.

"My case is unfair," the German national tweeted. "I was declined discovery, I didn't get my own data back, I need whistleblowers I am offering USD $5M."

Dotcom, whose Megaupload empire was shut down in January 2012, has long argued that US authorities, aided by close ally Wellington, illegally targeted him at the behest of Hollywood studios.

He told tech news website TorrentFreak.com that the multi-million dollar offer was aimed at helping him prove that allegation.

"We are asking for information that proves unlawful or corrupt conduct by the US government, the New Zealand government, spy agencies, law enforcement and Hollywood," he said.

"It is the opinion of my legal team that disclosure of such information would be lawful. I would also guarantee any whistleblower coming forward would have the best legal representation at zero cost."

Dotcom's extradition hearing is scheduled to begin in Auckland on July 7, although it has already been delayed several times amid legal wrangling over evidence disclosure.

If the 40-year-old and his three co-accused are sent to the US they will face charges of racketeering, money laundering and copyright theft carrying potential jail terms of 20 years.

Dotcom has launched a new venture called Mega while on bail.

The US Justice Department and FBI claim Megaupload and related sites netted more than $175 million in criminal proceeds, and cost copyright owners more than $500 million by offering pirated copies of movies, TV shows and other content.

Major music labels and the film industry in the US have also filed lawsuits against the file-sharing site.