In 2008, allowances paid to staff totalled $837,057, but that increased to $1.69 million in 2009.
Labour immigration spokeswoman Darien Fenton wants Immigration Minister Nathan Guy to account for the doubling in allowances, which she says "are out of kilter with the austerity the Government is expecting of every New Zealander".
"At a time when public sector staff numbers are being cut and all government departments are under pressure to make savings, blowouts like this in allowances and perks need serious answers," Ms Fenton said.
Last year, $844,344 was paid in expatriate allowances, $704,908 for hardship, $196,471 for cost of living and $136,310 in branch adjustment allowances.
"The total allowances trend was flat 2009-2011 as the cost of living allowance steadily decreased over the period due to a strong exchange rate and relative cost of living movements," an agency spokesman said.
"This decrease offset the increases in the expatriate and hardship allowances."
Immigration NZ is defending the amount it pays to its overseas-based staff, saying it used internationally recognised data provided by an independent organisation, Expatriate Conditions Abroad International, to ensure it has appropriate information and advice on conditions for staff based abroad.
"The department believes this is the fairest way of ensuring that staff are reasonably recompensed for working abroad," the agency said.
"Immigration New Zealand is a global operation and in 2010/2011 generated $108 million in revenue with 18 offshore offices as well as onshore staff."
The branch adjustment allowance is paid to recognise the differences in branch sizes and in risk or market profile, while the expatriate allowance is given as recognition of the disruption to a manager's life, such as disruption to their family situation arising from their offshore assignment, according to the spokesman.
The hardship allowance is to compensate for "any stress and upheaval" experienced as a result of working in an overseas environment.
Explaining the increase in allowances since 2008, the agency said it was caused by a change in the tax treatment of allowances by Inland Revenue.
"Allowances were grossed up for PAYE from the 2009 year onwards which caused the figures to increase at the time," the spokesman said. "The cost of living allowance in 2008 was also lower due to global economic conditions and a lower exchange rate."
Two new overseas branches, in Dubai and Ho Chi Minh City, were also opened in 2008.
In March, Immigration NZ spent more than $190,000 to bring 20 overseas staff to Auckland to attend a conference where Immigration Minister Nathan Guy outlined proposed changes for the agency.
ALLOWANCES
2008:
* Europe/Africa/Middle East - $186,444.50
* North Asia - $220,262.83
* Pacific - $141,913.49
* South Asia - $288,435.90
* Total - $837,056.72
In the 10 months to last month:
* Europe/Africa/Middle East - $315,611.26
* North Asia - $579,059.53
* Pacific - $266,239.83
* South Asia - $507,924.42
* Total - $1,668,835.04
(Source: Department of Labour)