Mining and Energy Union (MEU) members at the United Wambo mine near Singleton have voted in favour of protected industrial action, with more than 95 per cent voting yes to the proposal.
The result comes amid frustration with Glencore's bargaining position, including proposals for lower-tier classifications that the union says would undercut Same Job Same Pay outcomes.
MEU district president Robin Williams said the ballot result reflected a workforce that was paying close attention to what was being proposed.
"A 95 per cent turnout is an extraordinary result and shows just how strongly workers feel about the direction of these negotiations," he said.
"When around 70 per cent of the workforce votes in the first few hours, it tells you people are engaged, informed and paying attention."
"Workers have looked at what Glencore is proposing and they've responded accordingly. The company shouldn't be surprised by this result."
The United Wambo open-cut mine began operating in 2020 and is a joint venture between United Collieries (Glencore and MEU) and Wambo Coal (Peabody).
It produces thermal and semi-soft metallurgical coal for export.
Glencore did not comment on the latest developments.
Mr Williams said the ballot result should be viewed as a clear message from the workforce.
"This vote demonstrates that workers are united and determined to protect the standards generations of mineworkers have fought to establish."
"It should be a wake-up call for Glencore. The workforce is engaged, organised and standing together."
Mr Williams called on Glencore to negotiate a fair agreement that addressed workers' concerns rather than attempting to rewrite the rules.
He said the union was committed to reaching an agreement through negotiation, but workers have made it clear they expect meaningful movement from the company.
