Any rival offers for St.George would be unlikely to succeed after the Dragon's board agreed to pay Westpac a $100m break fee if it recommends any other offer.
The acceptance of a poison pill provision came after Westpac sweetened its all-scrip bid for Australia's fifth largest bank by promising St.George shareholders a special dividend of up to $1.25 per share - an increase of 28 cents a share from the previous offer.
"The St.George Board believes that the merger of St.George and Westpac, on the terms proposed, is a very positive outcome for St.George shareholders," said St.George chairman John Curtis. "The Independent Expert has informed St.George that the merger proposal is fair and reasonable and in the best interests of St.George shareholders."
A spokesperson for the bank said that the $100m break fee was reasonable given how far along the process is and the significant costs already incurred. She also pointed out that, since the merger was proposed in May, there has been many months for other interested parties to launch a counter bid.