The Serious Fraud Office has taken court action against Jami-Lee Ross over an inadvertent disclosure of a sensitive document.
The independent MP already faces criminal charges relating to two $100,000 National Party donations.
He and three others have pleaded not guilty.
But NZ Herald and Newstalk ZB has learned the Serious Fraud Office has filed an interim injunction against Ross.
It's understood the SFO inadvertently disclosed material to the defendants as part of its investigation, with one party indicating an intention to publish the information.
Both the Serious Fraud Office and Ross have been approached for comment.