ANZ Bank faces a $2.5 billion-plus claim from the billionaire founders of Burrup Fertiliser Pankaj and Radhikha Oswal after the bank allegedly forced the sale of their business for far less than they say it was worth and while they were under "duress".

Lawyer for the couple, Tony Bannon SC, told the Supreme Court of Victoria that ANZ Bank and receiver PPB worked together to ensure the business was sold for a base price to another of Burrup's shareholders, Norwegian group Yara, rather than for the highest price.

"The receivers made it clear to anyone who would listen that their sole purpose was to close out the debt," Mr Bannon said.

"Not only is it a breach of selling any asset rule 101 as it turns out it is the breach of the duty of the receiver," Mr Bannon said.