The site was put on the market without consulting the union.
An online petition is calling for a halt to the sale of Derrinlough Briquette Factory.
The site went up for sale last week, after operations ceased at the factory at the end of May.
SIPTU accused Bord Na Móna of breaking the terms of agreement entered over the closure of Derrinlough, by putting it on the market without consulting the union.
The petition has 140 signatures so far, and says the site's preservation should be considered on the grounds of the social and architectural significance of the last Briquette factory in Ireland.
You can access the petition here.
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