Wellington, Oct 7 NZPA - Investors will know by lunchtime tomorrow whether Westpac Banking Corp has to pay a tax and interest rate bill of $903 million.

The bank's shares were placed on trading halt today pending the judgment from the High Court at Auckland in the case, involving disputed tax on structured finance transactions.

Westpac told the ASX the judgment was being delivered this afternoon but would be subject to a binding order of the High Court, which prohibits publication until 10am Sydney time tomorrow.

The trading halt will remain until 11am Sydney time tomorrow unless Westpac makes an announcement before then.

Bank of New Zealand (BNZ) said in August it was appealing a case it lost in the High Court at Wellington, but it made a $661m provision for the case in its accounts.

"This is a complex area of law, and given the facts of the case, we're not convinced that the decision was the right outcome," BNZ chief executive Andrew Thorburn has said.

There has been speculation that the Auckland High Court, where more commercial cases are heard, may be more sympathetic.

IRD has yet to decide on potential penalties in the BNZ or other cases.

Five banks face more than $2 billion of disputed tax assessments for 22 structured finance transactions.

Apart from BNZ the other banks are treating the disputed tax as a contingent liability in their accounts, meaning it has not affected profit statements.

One of the banks' defences is that some of the transactions had binding rulings from IRD, which allowed interest and fees to be deductible and dividends to be exempt from tax.

The judgment against BNZ from Justice John Wild said a binding ruling expressly applied only to the transaction ruled on.

Westpac said in a statement to the ASX in July that its case involved amended assessments from IRD for the 1999 to 2005 tax years in relation to nine transactions undertaken between 1998 and 2002.

In the Westpac case the primary tax in dispute is about $586m, which with interest rises to $903m.

"All of the subject transaction in dispute were genuine financing arrangements with substantial corporate customers," Westpac said in July.

"Westpac obtained a ruling from the NZ IRD on another similar transaction in 2001 and the principles underlying the ruling are applicable in the disputed transactions," Westpac said.

IRD argued that the "tax tail wagged the commercial dog" in the transactions BNZ entered into with foreign counter parties.

Westpac shares last traded at $A25.51, ($NZ31.31) up 1.3 percent from the close yesterday.