Bord Na Mona Recycling has confirmed the sale to a Kerry company.
SIPTU is branding the impending sale of Bord Na Mona Recycling as an "act of economic vandalism".
The Union is now actively lobbying opposition and government TDs to halt the sale.
The semi-state company confirmed the sale to Killarney Waste Disposal Company for an undisclosed price over the weekend.
KWD were fined half a million euro last year for breaking regulations in the Waste Management Act.
SIPTU has already said they will ballot their members over strike action if the sale goes ahead.
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