In testimony last week, Fausto Tonna, the former Parmalat chief financial officer now under arrest, said that over seven years, some €70 million was paid to Parmalat in Tetra Pak discounts.
These payments rose sharply in recent years, from €5 to €6 million a year from1996 to 1999 to €15 million in 2000 and €30m in 2001 - when a third of the discounts were paid directly to the Tanzi family, and the other two-thirds to a Parmalat subsidiary, claimed Tonna.
Jürgen Haglind, a spokesman for Tetra Pak, confirmed that discounting was normal practice, but said he did not know if his company returned cash under such schemes, the Financial Times reported.
Tetra Pak has already cleared itself of earlier claims made by Parmalat executives to investors in November that it had issued promissory notes to the dairy group. At the time, Parmalat was seeking to offer reassurance of its financial health.
Investigators also suggest that some evidence from the dairy group's former executives is being driven by the desire to lay the blame for the crisis at one another's feet.
However, the latest claims of private payments from a trade supplier open the door to much closer scrutiny of the dairy group's trading relationships, and in particular arrangements that may have assisted in siphoning off Parmalat funds to private accounts.
The latest reports on the financial situation at Parmalat, following founder Calisto Tanzi's resignation and the company's move into bankruptcy protection last month, suggest funds missing from the group could total more than €10 billion and its debts €13 billion.
This has already placed pressure on the dairy group's relationship with Tetra Pak.
TetraPak has been inextricably linked to the astonishing growth of Parmalat over the last half-century. The Italian dairy giant was the first producer to use Tetra Pak's disposable cartons to package milk, and later became a pioneer of UHT (ultra-high temperature) milk, now packaged by Tetra Pak globally.
Parmalat still accounts for some 3 per cent of Tetra Pak's sales, and the dairy group has moved swiftly to keep its supplier abreast of its unravelling financial situation. One of the earliest steps taken by Enrico Bondi, the man charged with rescuing Parmalat, was to meet Tetra Pak's chief executive in Italy, Paolo Nigro, to brief him personally.
This followed Italian media reports that Tetra Pak was threatening to suspend supplies to Parmalat. Tetra Pak spokesperson Haglind said it was never his company's intention to cut off supplies. "But we will need to take some measures to secure our financial position - we need some kind of payment guarantees," he told Reuters news agency on 31 December.
"We intend to protect our financial interests, but we have been working with Parmalat for years and we intend to keep working with them," Haglind told Italian newspapers.Tetra Pak, headquartered in Lausanne, Switzerland, is a private family-owned company.