SIPTU has hit out at Tara Mines management, condemning their "abject failure" to agree to a facilitation process aimed at reopening the mine.
The union says management has reneged on an agreed plan for an independent process to resolve issues.
Workers at the County Meath mine have been temporarily laid off for 130 days, which the union describes as a "national scandal”.
SIPTU sector organiser John Regan said the Labour Court has now been asked to intervene.
"[Tara Mines owner] New Boliden unilaterally made the decision to put the mine into care and maintenance despite our best efforts,” he said.
“These included suggesting an independent facilitator to assist with the original 63 proposed changes to operational issues identified by the Group of Unions (GOU).
"The management's letter last Thursday confirmed that the company intends to stick with this approach and their own facilitator, thereby ruling out the joint facilitation process for which the Group of Unions had called.
"[We are now] urgently seeking a date for the reopening of the mine, an outline of voluntary redundancy terms and a request for a hearing of the Labour Court."
In June, Tara Mines temporarily announced 650 workers would be laid off after the low price of zinc and high energy costs meant the business had become unprofitable.
Laid off workers are entitled to social welfare and an additional €65 per week retainer fee paid by the company.
In a statement to Newstalk, Tara Mines said they did not think use of the Labour Court would be necessary.
“We are doing everything we can to re-open the mine as soon as possible,” a spokesperson said.
“We are working on the development of a rescue plan, designed to address operational challenges at Tara Mines, and want to work together with the group of unions on this.
“We will continue to engage with the group of unions.
"In order to help develop the plan, we agreed to hold a series of workshops attended by management, employees and union representatives.
"We believed the arrangements for the workshops were agreed by all parties, and we have agreed that the workshops should have an independent facilitator.
"We hope to resolve the issues regarding these arrangements swiftly, as we believe the workshops will be of benefit in the development of a rescue plan.
"We do not believe a reference to the Labour Court is necessary at this stage, although we will participate fully in the process.”
Main image: The Boliden Tara Mines in Navan. Photo: Mark Stedman/RollingNews.ie