At the same time, Westfield co-chief executive Steven Lowy has defended his father's plan to restructure the $70 billion property and shopping mall empire, dismissing criticism as ''a lot of hysteria''.

The fierce words come after Westfield Retail Trust (WRT) chairman Richard Warburton last Thursday deferred a vote on the proposal.

John Pearce, the chief executive of UniSuper, which holds more than 8 per cent of WRT, rejected the plan, saying it was too risky. Billionaire Frank Lowy hopes to split the Westfield empire's Australian and New Zealand shopping centres and related businesses from its international ones, combining them with the separately listed WRT to form a new internally managed Australian retail property group, Scentre Group.

But Mr Pearce said UniSuper bought into WRT because it was a landlord - not a developer or manager - of high-quality retail assets, which delivers attractive yields.

''Under the proposal, this vehicle changes; it becomes highly leveraged or much more leveraged, which is something that we don't want,'' Mr Pearce told Channel Nine's Financial Review Sunday program.

''All of a sudden it also takes on property risk, development risk and we're being asked to pay an exorbitant price for the privilege. So there's a couple of reasons we don't like it.''

Investors in WRT's bigger sister company, the Westfield Group, have strongly backed the proposal, with 97.26 per cent voting in favour.

But Westfield Retail Trust investors have been more cautious. They returned proxy votes totalling 74.1 per cent, just short of the 75 per cent threshold needed to approve the vote.

In an unusual step Mr Warburton had to adjourned the vote for up to two weeks, just as Frank Lowy warned that he will proceed with the plan to split the Westfield Group regardless of whether WRT voted the deal down.

Mr Pearce refused to weigh into bullying accusations aimed at Mr Lowy.

''I've got the highest regard for the Lowys and Westfield as managers. We've bought into a vehicle with entrenched management rights and Westfield is that manager - very happy with that.

''What I think this tells us is unequivocally, if indeed we have some sort of split and there's a new Scentre Group that does not have the WRT assets, I think what we're seeing here is the need for a totally, a truly independent board from WRT.''

He said the vote should not have been delayed because ''it was pretty clear which way the vote was going to go'', and people should not ''read too much'' into the 74 per cent of WRT shareholders who supported the restructure.

''A lot of the 74 per cent also own Westfield Group, so they're seeing a transfer of wealth from WRT to WDC; of course they'll vote for the transaction.''

But Steven Lowy said the 74 per cent of votes did matter and that a restructure would benefit WRT shareholders.

''I understand the division and also some of the hysteria, and also the great focus on the Lowy family and my father, but that's a lot of hysteria going on,'' Mr Lowy told Financial Review Sunday.

''We're proposing the restructure really because the Westfield Group has been in transition over a number of years, where it has returned capital to investors, where it has repositioned its portfolio and it felt in 2013 that it was now in a position to separate the international business from the Australian business because both of those businesses would stand on their own,'' he said.

''We felt it was in the interest of WRT shareholders to offer [the merger] … because we felt that the Scentre Group ultimately would be a much better investment than WRT shareholders have today.''