4000 staff members from the Ministry of Business, Innovation and Employment (MBIE) and Inland Revenue (IR) staff will take strike action on two separate days next month.
On July 9 and July 23, staff members at both agencies will stop work for two hours.
The Public Service Association (PSA), which is the union representing workers in the sector, says there was an "overwhelming vote" to strike.
- Nurses to strike across the country
- Unions threaten to block Wellington buses
- Supermarket strike called off after 'significant' wage increase
PSA national secretary Glenn Barclay said: "Our members are very reluctant to take this step, but they feel they have no choice - and the level of support in the vote shows the level of frustration."
He said MBIE was spending millions on contractors while denying PSA members a living wage.
PSA National Secretary Erin Polaczuk said IR members have not taken strike action in 22 years, which shows they're at breaking point.
"Our members take their jobs very seriously and they're trying desperately to keep the system on track while IR presses ahead with its Business Transformation project which will see one in three staff let go by 2021."
Ms Polaczuk said the Best Start tax credit, which starts on July 1, will need to be processed manually in IR's systems, and that will "drastically" increase the workload of staff.
"To have all this happening while the employer refuses to consider a modest across-the-board pay increase is deeply upsetting to our members."
The PSA will notify both agencies of the strike action.
"We hope MBIE and IR will take the level of support for this action very seriously, and come back to the negotiating table ready to listen," Mr Barclay said.