The $11 billion merger will be before the Australian Competition Tribunal next week after Tabcorp took the unusual step of withdrawing from the Australian Consumer and Competition Commission's approval process in March, before the watchdog had made a final decision.

The move caught the ACCC by surprise, a day after it handed down a preliminary finding which largely waved-through the takeover but also flagged some competition concerns.

In its opening submissions to the tribunal Tabcorp dismissed those concerns, arguing that the supposed victims of the merger's anti-competitive effects did not agree with the ACCC that they would be harmed.

"It is difficult to imagine more powerful evidence that the ACCC's theories are not connected to reality," Tabcorp submission says.

"The Tribunal would be very slow indeed to conclude that all of these people do not know their industry, or are incompetent or confused."

Tabcorp says the racing industry in all states expect Victoria supported of the merger, and the only objections came from rival commercial interests.

The wagerer accuses the ACCC of being "captive" to Racing Victoria and Racing.com, which is owned by Racing Victoria and Seven West Media.

Tabcorp owns broadcaster Sky Racing, and concerns were raised about it leveraging that power through Tatts retail outlets. It was feared Tabcorp could influence the level of betting on certain races by broadcasting that race on another channel or by not putting it to air.

But Tabcorp says that issue exists pre-merger, and that the suggestion it could use Sky Racing to manipulate betting was "creative speculation".

"It is apparent that some industry participants are dissatisfied with various aspects of the way in which aspects of the industry operate today and seek to enlist the Tribunal to effect changes in their commercial interests," the submission says.

Tabcorp will be able to argue in favour of alleged public benefits of the merger when it comes before the tribunal. The ACCC ruling would have been based exclusively on whether the deal was likely to substantially lessen competition.

The ACCC has a statutory role in assisting the tribunal by making a submission and cross-examining witnesses.

The Victorian, NSW, Queensland and South Australian racing industries get a bulk of their funding through deals with Tabcorp and Tatts, and Tabcorp says its corporate competitors such as CrownBet and Betfair have "exploited" their cost advantage and drawn funding away from racing industries.

Merging Tatts and Tabcorp would create a stronger and more efficient company, which would therefore benefit the racing industries that depend on their revenue, Tabcorp says.

The ACCC statement of issues found the deal would not lessen competition in wagering because there was limited overlap between the two companies' brick and mortar outlets and in light of the proliferation of online bookmakers.

Tabcorp agreed to sell its Odyssey Gaming business to appease the ACCC's concerns about a concentration of the poker machine market.

A spokesman for the ACCC said the commission would not comment on matters before the ACT.