Bankia, which was bailed out in 2012, is accused of misrepresenting its accounts ahead of the flotation and hundreds of customers who say they lost their money after converting their savings to shares have brought separate lawsuits against the group.
Last month Spain's Supreme Court said "serious inaccuracies" in the information provided by Bankia for the listing led investors into error - opening the way for hundreds of millions of euros in compensation.
The Supreme Court said that small shareholders had no source of financial data on which to base their decision to buy shares except what Bankia told them.
Jose Plaza, the lawyer for the 660 shareholders, asked a Madrid court Thursday that they be reimbursed the 6.3 million euros they invested in Bankia shares, plus interest.
The ruling has been postponed to a later date. Former IMF head Rodrigo Rato, who was chairman of Bankia at the time of the listing, is also being investigated, in separate proceedings, along with other suspects.
Bankia and its parent company BFA said in December they had set aside €1.8 billion in provisions for claims that by the end of 2014 already stacked up to €819 million.