The Public Service Association, which represents about 400 Statistics NZ workers, supported the day of strike action, which also took place in Auckland and Christchurch.
"Our members are expert statisticians, but even they find their pay system needlessly complex," said PSA national secretary Richard Wagstaff.
"There is some irony in the very workers who calculate CPI not being able to keep up with it. Statistics have refused any across-the-board pay increase, leaving staff falling further behind the cost of living."
Statistics NZ deputy chief executive Kelvin Watson said he was restricted by the laws around collective bargaining to discuss details of the offer.
"We can say we are disappointed that our offer hasn't been recommended to staff by the PSA, and that its average performance-based 3 per cent rise is generous relative to other public sector settlements.
"We must also stress that we are keen to continue negotiations. We hope that we can resolve this soon because, like our staff, we want to reach an agreement."
The current collective agreement expired on February 19 but it can remain in place for up to 12 months while a new agreement is finalised.
More strike action is planned for two weeks' time if the deadlock continues.
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