Its listing in German financial hub Frankfurt is supposed to take place before the U.S. Thanksgiving holiday on November 28. "But the whole thing could slip by a day or two," one source close to the deal told Reuters on Tuesday.
The deal will float more than 50 percent of the Austrian group's shares and is expected to raise between 600 million and 800 million euros, one of the sources said.
That would value the group at around 1.5-1.6 billion euros, a slight discount to larger rival Amcor (AMC.AX) based on operating profit.
The listing begins the exit of OEP, which owns around 73 percent of Constantia Flexibles. The company itself is set to get 150 million euros from the deal to finance future acquisitions, the sources familiar with the matter said.
For tax reasons, OEP will contribute 50 million of this in advance of the deal.
The Turnauer foundation that owns 23 percent has pledged to at least maintain its stake, so will have to buy some of the shares offered in a capital increase accompanying the IPO.
A second listing on the Vienna Stock Exchange is planned.
Deutsche Bank (DBKGn.DE), Goldman Sachs (GS.N) and JPMorgan (JPM.N), the parent of OEP, are running the transaction. They and Constantia declined to comment on its details.
JPMorgan announced in June that OEP would in future have to raise its own funds.
Constantia Flexibles said last month it planned a stock market listing by year's end.
The company makes packaging for food and pharmaceuticals and labels for bottles. It has 8,200 employees and competes with Australia's Amcor and Bemis (BMS.N) and Sealed Air (SEE.N) of the United States.
Its customers include chocolate maker Mars, French food group Danone (DANO.PA) and Italian confection maker Ferrero.
It made sales of 1.23 billion euros in the first nine months of 2013 and posted adjusted earnings before interest, taxes, depreciation and amortization of 175 million euros.
