The Earthquake Commission has heightened security at all its offices after it received an anonymous letter which threatened the safety of staff.
Police are investigating the threat which references the Christchurch mosque shootings.
No further details have been released but the commission said there had been repeated threats including one on 1 May that threatened staff safety.
EQC said it did not target a particular building or address but it was increasing security for staff across the country.
Its deputy chief executive, Renée Walker, said people may experience personal stress or feelings of anger following a natural disaster, or in response to interactions with EQC, and unfortunately a very small number choose to display behaviour that was threatening or offensive as a result.
She said anyone with information that could help identify the person responsible should contact the police.
"There is no excuse to abuse, threaten, or even assault EQC staff and those working for us. While we may not always get things right, our people turn up on a daily basis to try and help people in the best way they know how," Ms Walker said.
"Our team is supporting police in any way we can with their investigation. If anyone has any information that can help identify the person who sent this letter, we strongly advise they contact police."
EQC Minister Megan Woods said she's aware of the threat.
"I understand a bullet was sent to EQC more than two years ago, and there is potential that the bullet was sent by the same person who has made the recent threat. This is part of the police investigation," Ms Woods said.
