More than 80 workers are refusing to use a troublesome kiln at Pan Pac Forest Products' mill, north of Napier.
The kiln has been repeatedly shut down due to health and safety breaches and concerns about the gas emissions. Last week four workers from the Whirinaki site required medical treatment.
Workers from the lumber division have issued a health and safety strike notice effective from 10am yesterday. They would not load wood into the Thermally Modified Timber kiln. The strike notice covered 85 union members.
First Union general secretary Robert Reid said members were fed up with repeated health and safety issues with the company's new kiln.
The kiln was introduced in April 2014, but a year later workers and the neighbouring community reported outbreaks of rashes, breathing problems and other ailments that they feared were linked to emissions from the kiln.
WorkSafe issued Pan Pac with a prohibition notice and the kiln was shut down for testing, Mr Reid said.
"WorkSafe eventually lifted the prohibition notice, but problems have continued."
Last week the kiln malfunctioned and emitted toxic fumes that hospitalised four workers, one worker even became unconscious.
At the time, Pan Pac general manager Doug Ducker said the incident was a fault of a particular valve and that the kiln had been operating for the past few months with no issue.
In August, authorities said tests showed levels of air pollutants were well below recommended guidelines when the kiln was operating normally.
But they suggested acrolein and acetic acid levels could exceed standards if a burner used to eliminate noxious gases stopped working during the kiln operation.
Mr Reid said every worker deserved to arrive at work knowing they'll be safe.
"Workers should knock off work knowing they aren't taking dangerous chemical residue home."
First Union organiser Mike McNab said workers had made their concerns known to the company and to WorkSafe on countless occasions.
"This is not the first time a serious health and safety breach has happened and workers fear it won't be the last. They need to have some control over not working in unsafe conditions, the health and safety strike gives them this."
Although the kiln is currently under lockdown pending an investigation, union members have lost all confidence that the kiln can be operated safely, Mr McNab said.
"The health and safety strike action will only be lifted when members are confident that their workplace is safe and vote to lift it."
PanPac is owned by the Japanese company Oji Paper.