The war between James Packer and local gambling rival Echo Entertainment has been reignited by claims that the plan to accommodate the billionaire's $1.5 billion casino resort at Barangaroo is legally flawed.

Legal advice provided to the planning department by Echo Entertainment, owner of The Star casino, says the application to modify Barangaroo's concept plan to include Crown Sydney's 69-storey tower would be open to court challenge.

The submission has prompted a furious response from chief executive of Crown Sydney, Rowen Craigie.

"I consider this a blatant misuse of the planning process by The Star casino to try and protect their existing monopoly and delay much-needed competition into Sydney's VIP gaming market," Mr Craigie said in a statement.

The advice, by Adrian Galasso, SC, and Clifford Ireland, questions the scale of the environmental impacts of the new proposal given the increased height and density of the buildings proposed for Barangaroo South under the plan.

The new concept plan would mean a 7.4 per cent increase in gross floor area for Barangaroo, including lifting the height of Mr Packer's hotel and casino building from 168 metres to 275 metres.

The advice suggests the government's decision to grant Mr Packer a casino licence before the concept plan application is considered puts in doubt the Planning Minister's ability to be impartial in his decision-making.

The advice also questions if NSW liquor and gambling authorities, the health department and the department of community services should have been consulted as they are "arguably relevant in relation to a proposal for a casino".

"[The modification] if granted, would be open to judicial review proceedings ... of the Land and Environment Court's jurisdiction," the advice says.

The advice is attached to Echo's objection to the concept plan, revised after former premier Barry O'Farrell asked developer Lend Lease to relocate a hotel over the harbour in the initial plan following community objections.

Lend Lease struck a deal with Mr Packer's Crown Resorts to build a new hotel building on Barangaroo South. Crown insisted this could only be financially viable with a casino licence.

The casino application sparked a war with Echo, which has an exclusive Sydney casino licence at the Star until November 2019. Echo pitched a rival plan to redevelop the Star, but the government chose Mr Packer's proposal.

Also attached to the Echo submission is a letter from planner Deborah Laidlaw that also questions whether the inclusion of a casino in the new hotel building can be "properly regarded as within the scope of a 'modification' ".

Echo Entertainment's chief executive and managing director, Matt Bekier, says in a covering letter that the company believes "the need for transparency is paramount" to ensure public confidence in casino developments.

"The enclosed advice and assessment raise matters which therefore should be fully considered and addressed, as would be the case in regard to any planning application," he writes.

A spokeswoman for Lend Lease said the company will review the submissions and "respond in detail to the points raised to the NSW Department of Planning and Environment".