Negotiations with the company that began in February have deteriorated after the combined Australian Manufacturing Workers Union (AMWU) and Electrical Trades Union members rejected their final offer, AMWU lead organiser Brad Pidgeon said.

"Industrial action is the last resort, but with cost-of-living pressures remaining high, our members are asking for a decent wage to help alleviate the pressures on them and their families," he said.

"Tomago's highly-skilled maintenance workers are also seeking parity on other conditions with production workers onsite.

"Members of the combined unions have looked after the company during the most extreme of hard times - not only during COVID but for many years leading up. They only want what is fair and reasonable."

Tomago is Australia's largest aluminium smelter, and is part-owned by Rio Tinto, producing up to 600,000 tonnes of saleable metal each year.

He said the unions would back their members to achieve a 'fair outcome' - saying Tomago's offer was only 11 per cent over the term of a two-year agreement.

That's six per cent in year one and five per cent in year two, which he called 'well below' the consumer price index of 7.8 per cent.

Tomago Aluminium chief people, safety and environment officer Natalie Britt said the company has been negotiating in good faith to reach an agreement with its maintenance and trades employees.

"Tomago respects the rights of its employees to undertake protected industrial action and that process will take its ordinary course," she said.

"Tomago is committed to providing employees with fair and reasonable entitlements, that supports our culture which is both inclusive and performance-driven."

She said the company wouldn't comment on the specifics of the negotiations but said that it had put measures in place to minimise any disruptions to business and clients and prevent health and safety risks if industrial action was taken.

"Tomago remains committed to ongoing negotiations with its workforce and their representatives to reach an agreement which is approved by the majority of employees and delivers a fair and reasonable outcome for all parties," she said.

Earlier this year it was announced that Tomago Aluminium and three other manufacturers would be supported to transform into low carbon facilities as part of a partnership agreement with the state government.

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