Spy boss Ian Fletcher has apologised to Prime Minister John Key for his agency bungling its report to Parliament on the level of its surveillance.
The Government Communications Security Bureau (GCSB) was forced to release an amendment to its annual report, which saw an increase in the number of interception warrants and access authorisations for the 2012-13 financial year.
A total of 11 interception warrants were in force for that year, up on the original amount which was reported at seven. Five interception warrants were issued, corrected from four.
A total of 26 access authorisations were also in force, compared to the originally-thought 14, and 11 were issued rather than nine.
A spokeswoman for Key said the prime minister was "unhappy" about the error and had received an apology from Fletcher, the GCSB director.
"The prime minister has been advised that the error stems from GCSB mistakenly counting the number of operations rather than the number of warrants on issue.," the spokeswoman said.
"There was no attempt to deliberately mislead,. Further, he has been advised by the director that steps have been taken to ensure the error cannot happen again."
Greens co-leader Russel Norman said serious questions needed to be asked.
"This is another serious mistake by the GCSB, which raises real questions about their ability to carry out their job," Norman said.
"The most generous interpretation is that the bureau was confused about their legal reporting obligations.
"This mistake is not a small technical issue. It cuts to the heart of their accountability to the Government and the New Zealand public."
Labour leader and security and intelligence spokesman David Cunliffe said the blunder was "embarrassing".
"Interception warrants by the bureau have been under the spotlight for the past two years following the raids on the Dotcom mansion," he said.
"It is mindboggling the GCSB couldn't get the number of warrants it's issued correct in its annual report."
He backed calls for an inquiry to be held into the spy agency, saying Key - the minister in charge - should "hang his head in shame".
Is it time for Judith Collins to go?Related story: Judith Collins looking isolated