The order signed to suppress the involvement of the GCSB in the Kim Dotcom case was the only one of its kind made in the last decade.
The spy agency has stated that the certificate signed by Finance Minister Bill English as Acting Prime Minister was the only one found in "a thorough search of our files".
Mr English was asked by the GCSB to sign the "ministerial certificate" while Prime Minister John Key was overseas in August. The certificate said knowledge of the GCSB's involvement in the Dotcom investigation would damage its ability to detect or prevent serious crime.
The fact it was the only ministerial warrant in 10 years was discovered by the Green Party under the Official Information Act. Its rarity has led Green Party co-leader Russel Norman to question how Mr Key stayed ignorant of its existence until a month after it was signed.
Mr Key was only told after it emerged the GCSB's spying on the internet tycoon was illegal - a discovery which ruined the GCSB's bid for secrecy.
"It shows it was an extraordinary event. It was a one-in-10-year event. You would think he would tell the responsible minister when he returned from overseas."
Dr Norman said the rarity of the event also raised questions about the level of knowledge inside the GCSB.
"Why on earth did they get him to sign it? Was it because they already knew it was illegal?"
Mr Key ruled this out in Parliament. He said the GCSB asked for its name to be withheld because it believed it had acted legally.
"It also had the paperwork to support that. I have seen that paperwork, and the paperwork made it quite clear it believed its activities to be legal," he said.
Dotcom: law suit to red suit
Kim Dotcom has been signed up for a Christmas pantomime called Mega Christmas. The name is a tribute to Dotcom's filesharing business.
Oliver Driver, Dave Fane, Mia Blake, Jennifer Ward-Lealand and Kimberley Crossman are among well-known names starring in the adult-themed panto. A character has been cast to play Dotcom with the tycoon filming a segment to be shown during the performance.
Basement Theatre's Charlie McDermott said it was hoped Dotcom would appear live on the opening night.