Tasmanian members of the Australian Education Union say they won't administer the national literacy and numeracy test, taken by children in years 3, 5, 7 and 9.
Striking teachers also won't support NAPLAN testing in any capacity or conduct any practice tests for 2026 and 2027, the union says.
The window for the national test, which provides a snapshot of performance against Australian standards, is March 11-23.
Teachers and other unions have been at loggerheads with Tasmania's Liberal government over pay and negotiations, along with looming public sector job cuts aimed at curbing state debt.
"Our members are quite angry," said David Genford, the union's Tasmanian president.
"We're instructing members that if they're asked to cover classes, do printing, any type of preparation, to politely say no.
"There may be some schools where it is able to go ahead.
"But schools that have the strong union density, and that is most of the schools out there, you're not going to see the NAPLAN tests take place."
The union said it wanted to land a "devastating blow" to the government, with escalated action such as school closures on the cards by the end of March.
Teachers and support staff want the government to match a deal accepted by the state's police force in December which included additional allowances, Mr Genford said.
The NAPLAN stop-work action could be avoided if an improved offer is forthcoming, he said.
Education Minister Jo Palmer said it was disappointing the union had decided to take industrial action that impacted learning.
"Our top priority will be to ensure we can minimise disruption and the impact on student learning," she said in a statement.
The government was committed to delivering fair and affordable agreement through respectful and constructive negotiations, she said.
The government has said it wants to cut 2500 public sector jobs in a bid to reign in ballooning net debt that Treasury says could reach $146 billion by 2040 without corrective action.
Thousands of public workers held a rally in October, while health, child safety, biosecurity and forensic science staff have been among those to stop work in recent days.
The state education department has been contacted for comment.
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