A security review of Work and Income offices is being carried out following the double shooting at an Ashburton office on Monday.
That would mean some offices would be "locked down", Social Development Minister Paula Bennett said today.
Over the past few days the department had seen the best and worst of people, with some making threats against offices around the country, Ms Bennett said.
"We've taken those threats very seriously.
"In some circumstances that will mean us locking down sites - that means other people that genuinely need help are not able to get it as quickly or as efficiently as they require it.
"But those are the steps we are well prepared to take."
Ministry of Social Development chief executive Brendan Boyle said former police commissioner Robbie Robinson and Deloitte New Zealand chairman Murray Jack would be undertaking the review.
"It'll be an independent review into our security protocols."
Mr Robinson and Mr Jack would be supported by an advisory group, which included PSA national secretary Glen Barclay and ANZ Bank chief operating officer Craig Sims who had experience with security issues, Mr Boyle said.
"The team will also access specialist security expertise at their discretion."There were two objectives for the review, Mr Barclay said.
"The first is, were all practical steps taken to ensure the safety of our employees in relation to the shooting at the office, given our functions and activities and the risks associated with those.
"The second is, what changes are recommended for the physical security environment in the ministry workplaces to ensure the physical safety of the staff and members of the public against threats."
From Monday security guards would be posted at the doors of service centres and could ask for identification from people wanting to enter the building, Mr Boyle said.
"If anyone is identified as presenting risk they may be refused entry.
"While that may cause some slight inconvenience to clients, we believe in the interests of safety for both staff and clients, this is a step that's important to take."
Security guards were already posted in all service centres, and an extra 108 had been added this week - meaning some centres had two or three guards posted in the building, he said.
The Ashburton office was hoped to be opened again soon, staffed by employees from other offices, he said.
Since Monday there had been numerous incidents at sites around the country, including phone threats and a smashed window.
As well as the extra security staff at sites around the country, police were also based in or near all Christchurch Work and Income offices.
Earlier today, former Work and Income chief executive Christine Rankin said the possibility of a tragedy like the Ashburton shootings had always hung over staff.
Ms Rankin told TV3's Firstline that Work and Income staff deal with people in stressful situations that can't be "de-escalated or simply talked through".
"We've always thought that something like that could happen, it definitely hung over all of the staff there for a long period of time."
She said when she was chief executive someone drove a car through a Work and Income office in Flaxmere.
"It was very lucky that someone wasn't killed in that incident and that did give us a shock and thought about the reality of the thinking that something really big could happen."
Ms Rankin said that removing all barriers in offices in favour of open-plan style had decreased the number of incidents of violence.
"The minister and the chief executive must be really worried now about what they're going to be forced to do, because in most other parts of the world the staff are behind bulletproof glass," she said.
She said she hoped that New Zealand would not end up in that situation.
Russell John Tully has been charged with two counts of murder and one count of attempted murder.
Security has been beefed up at Work and Income offices nationwide.
One hundred security guards were being deployed at branches around the country after alleged threats in the aftermath of the Ashburton shootings.