Tatts shareholders had been due to vote on the proposed tie-up next month, on October 18, but that timeframe appeared to be shot down on Tuesday when the national competition tribunal ordered further hearings starting on October 24.

The tribunal is reconsidering the mega-merger after the competition watchdog won a Federal Court appeal against an initial approval.

Neither Tabcorp nor Tatts had made an announcement to the stock market by 4pm about what the latest tribunal orders would mean for investors.

The delay is the latest setback for the two gaming giants, after the Federal Court last week found the tribunal's original approval decision from June was potentially flawed, must be "set aside" and sent the matter back for review in front Australian Competition Tribunal president John Middleton.

The court sided with arguments made the national consumer and competition watchdog that the tribunal's decision had wrongly overlooked concerns surrounding the immense market power that the merged Tabcorp-Tatts entity would command, and the subsequent lessening of competition.

But in a win for Tabcorp on Tuesday, Justice Middleton agreed to accelerate the timeframe for the re-application process, which, if successful, means the two companies may be able to seal their merger before Tabcorp's offer officially expires.

"We've got to proceed as quickly as possible, but with all due process," Justice Middleton said.

In a bid to expedite the matter, Justice Middleton added that he may take mainly written submissions and limit the roles of "intervenors" in the case, including rival bookmaker CrownBet, which objects to the merger approval.

"I was very generous [in the original application process] in allowing the intervenors in taking a full role," he said. "I'm not currently disposed to allow the intervenors to have this same 'open-door' policy."

Justice Middleton had previously flagged doubts over whether his tribunal had the power to reconsider the merger case due to a time-limit contained in the legislation.

But he decided on Tuesday to run a dual track process where he would concurrently hear both a review of the original application, and an entirely fresh application.

That structure would cater for the possibility that the tribunal's jurisdiction was challenged.

CrownBet, in its submission, urged the tribunal to take into account significant competition changes in the wagering market since it granted the original approval, which had affected digital bookmakers more than traditional gambling companies.

These include bans on in-play betting, and the added impost of a 15 per cent "point of consumption" tax for online bookmakers in South Australia and Western Australia, which is gaining momentum in other states.