Immigration New Zealand is apologising after sending emails mistakenly informing people their visas had been extended.
It sent emails two days before Christmas with news about the automatic extensions.
But in another email, sent on Friday, it said partners and children of certain visa holders should not have been included.
Immigration New Zealand (INZ) said about a third of the 13,000 people who were sent an email about visa extensions should not have received it. It would be emailing them soon to clarify their situation and apologise.
INZ general manager of enablement Stephen Dunstan, said an administrative error meant that partners and children of visa holders who were not eligible for a visa extension received the email last month.
The recipients would have been able to check the criteria to see if they were eligible, but Dunstan said some people may have been confused and found the mistaken information stressful.
"Due to an administrative error, the group of partners and dependants also included those who hold visas based on a relationship to a visa holder who would not have their visa extended under the special direction, and therefore the partner or dependant does not qualify for the extension either."
The email also referred to another error in October, in which Exchange Work visa holders were mistakenly added to a mailing list about seasonal work visas for working holidaymakers.
Immigration lawyer Mike McMellon said the errors were significant.
"This really is bad," McMellon said.
"Some people, thinking their visas had been automatically extended, may not have applied for new visas. Their visas may have expired and they may now be in New Zealand unlawfully.
"Similarly, somebody's visa may be about to expire and now they have to scramble to try to put a new visa application in place before the current visa expires. Now, depending on the amount of time they have before their current visa expires, that visa may not be very well prepared and they might be declined on the basis of that.
"Others whose visas are expiring may not appreciate they need to take action, perhaps very urgent action, to renew their temporary visas so they don't become unlawful."
It appeared INZ's email before Christmas was sent directly to immigrants, when it should have been sent to their adviser or lawyer who may have been able to raise questions about its accuracy, McMellon said.
Also compounding the problem was not being able to check on extensions because those visa updates were still being carried out and would not be complete until March.
"That is kind of problematic because you have to cross your fingers that will actually happen, and that you will be recognised as having had your visa extended. Difficult for employers as well, as they can be in the gun if they're employing people who aren't entitled to work."
It was hard to know how many people had received the email in error and how many would lose their chance to stay as a result, McMellon said.
"But even if it's just one person, that's an incredible upheaval in that person's life, and potentially the lives of the families as well. If your visa has expired because you've relied on Immigration New Zealand's advice, you're in a very difficult position, potentially here unlawfully and you're going to have to regularise your immigration status," he said.
"INZ's communication makes it clear INZ is not giving those prejudiced by INZ's mistake any leeway. In all honesty I don't think that's good enough.
"Migrants are under incredible stress at the moment experiencing massive uncertainty. Significant errors of this nature from INZ add to that uncertainty.
"I think if you received an email from Immigration New Zealand, saying that your visa had been automatically extended and you relied on that information to your detriment, then I think immigration should honour their position and grant that extension."
But INZ included a frequently asked questions section on what would happen to those who believed - due to the email - that they were eligible for an extension and were not.
"The email that INZ is sending to those who received the 23 December email in error will explain that if an individual's visa does not meet the extension conditions, it is important they apply for another visa before this expires or arrange to depart New Zealand," INZ's Stephen Dunstan said.
"Any individuals whose current visa has expired and they did not apply for a further visa due to thinking that they would get the extension because they received the 23 December email in error will need to request a visa through the section 61 process. They should contact INZ as soon as possible to discuss their situation."
The email also outlined how the mistake happened, however it only sets out which visa categories are not affected:
"Due to an administrative error, the list of partners and dependent children emailed regarding the extensions also included those who hold visas based on a relationship to a visa holder who did not have their visa extended under the special direction," it said.
"INZ is contacting visa holders who received emails in error to clarify eligibility and apologise for any confusion caused, and to advise how they can check their immigration status.
"Who does this email error impact? Partners and dependent children of work or student visa holders where the partner or parent (principal visa holder) does not hold one of the visas listed (and expiring between 1 January and 30 June 2021) will not have had their visa extended."
• Essential Skills Visa • Some Work to Residence Visas • Special and Skilled work visas for China, Indonesia, South Korea, Philippines and Vietnam • Special category work visas for Japanese Interpreters and Thai Chefs • Employer-specific work visas granted under section 61 of the Immigration Act 2009 • Fishing Crew Visa • Religious Worker Visa • Silver Fern Practical Experience Visa