The TUC and organised labour following a consultative meeting are now set to file a suit at the Fast Track High Court here in Accra to reverse the sale.
There are four representatives of organised labour on the SSNIT board that initially approved the 90 million cedis deal.
SSNIT as the majority shareholder had approved the deal granting private equity firm, Fortiz a 90 per cent stake in Merchant Bank.
The Secretary General of the TUC, Kofi Asamoah told Joy News although they were part of the SSNIT board that approved the deal; there are now fresh disclosures that make it impossible to stand by the sale.
Mr Asamoah said the decision to go to court was also strengthened by the fact that both the Bank of Ghana and SSNIT were not prepared to meet organised labour to discuss concerns raised against the sale.
He said the two institutions were unwilling to discuss the matter with organised because the case was already pending in court.
He would not however disclose the details of the fresh evidence, adding, everybody will know what the evidence is once the matter is sent to court.
If organised labour carries out its threat to go to court, it will be the second time the controversial sale of Merchant Bank will be challenged at the law court.
Andrew Awuni who is with the Centre for Freedom and Accuracy is on appeal after a Commercial Court ruled that he did not have the capacity to challenge the sale of Merchant Bank to Fortiz.
Speaking to Joy News, a legal practitioner Rockson Nelson Dafeamekpor said organised labour is likely to face the same hurdle as Andrew Awuni.