The Lowy family faces an uphill battle to convince investors in their Westfield shopping centre empire to back a controversial plan to split the company.

Westfield shareholders are preparing to vote on Thursday on the plan that would spin off the group’s Australasian shopping centre business into a separate company from its offshore operations.

Under the plan, the Australian and New Zealand business would merge with the separately listed Westfield Retail Trust (WRT) to create a new entity, Scentre.

Westfield Group’s international business would become Westfield Corporation.

But the plan faces stiff opposition from the Australian Shareholders’ Association and Westfield’s major investor, UniSuper.

The ASA argues the proposed split favours Westfield Group to the detriment of WRT investors.

“There’s a fair chance that the proposal will be voted down. The biggest shareholder, UniSuper, is against it on behalf of 450,000 university workers,” ASA representative Stephen Mayne told AAP.

“I think there will be others who will vote against it.”

Westfield needs support from 75 per cent of shareholders who vote on the planned split to get the deal over the line.

Shares in Westfield Group and WRT have been placed in a trading halt ahead of the vote.

Shareholders in both entities will vote on the plan at separate meetings in Sydney.