The Construction Forestry Mining and Energy Union is also prepared to argue in the courts that the disparity at Blair Athol in Queensland is discriminatory, its district vice-president Glenn Power told ILN.

“It is a bitter pill to swallow for some of our members,” he said.

“One of our members has been there for 29 years. We have calculated that the disparity with his redundancy package would be in the order of $100,000.

“Some of these blokes are retiring now and they have given their heart and soul to that mine.”

About 30 employees, or a quarter of the mine’s total workforce, are affected by the lower redundancy packages.

Mine workers at Blair Athol receive a base rate of pay, a market allowance and a role allowance that varies depending on the shift worked and the employee’s position.

Employees with staff contracts that were negotiated in 2007 have a role allowance included in their redundancy payouts.

The role allowance can range from $2500 to more than $25,000 annually but only non-union employees are being offered the role allowance when the final redundancy payout is calculated, according to Power.

Rio Tinto respects the right of employees to choose whether or not they take protected action, a company spokesperson told ILN in a statement.

“However, Rio Tinto has bargained in good faith regarding the Blair Athol Mine Workers Enterprise Agreement and is disappointed the CFMEU has chosen to encourage industrial action in the final weeks of the operation,” he said.

“Employees who have chosen to be on this collective agreement have benefited from a number of secure working conditions and benefits over many years. Rio Tinto believes the proposed agreement as a whole, including the redundancy payments, are fair.

“We have plans in place to minimise disruptions using the remaining workforce and operations at Blair Athol are expected to finish as scheduled this month.”