Facebook Inc wants a federal judge to throw out a case linked to the Cambridge Analytica scandal, arguing it may run Facebook.com but another company serves Australian users.
The US firm and Facebook Ireland are being sued by the Australian Information Commissioner over alleged breaches of 311,000 Australian users' privacy, with the watchdog saying Facebook Inc serves Australians.
But a representative for Facebook Inc pointed to agreements with users that state the website Facebook.com was being offered to Australia by Facebook Ireland.
"It's clear two businesses are being run through the same website," Noel Hutley SC told a preliminary hearing on Friday.
He also pushed against the argument the firms' use of materially-identical terms and conditions inferred Facebook Inc was conducting a global business through subsidiaries.
"It's not a question of inference, it's a question of fact," Mr Hutley said.
"The mere fact the same contract is used for two different documents is no more than a common set of circumstances run into by businesses every day in this world."
Both entities are accused of disclosing the personal information of Australian Facebook users to third-party app This Is Your Digital Life between March 2014 and May 2015.
Cambridge Analytica later used data collected by the app for political profiling purposes.
Cambridge Analytica rose to global prominence in 2018 when it was linked to a breach using Facebook user data for political advertising.
The information commissioner needed to establish in the Federal Court that Facebook Inc carried out business in Australia and that the personal information subject to the case was collected and/or held by the US firm in Australia, Mr Hutley said.
But it wouldn't and couldn't - in part due to a "rigid" division between the two companies, he added.
The commissioner had no evidence Facebook Ireland operated on behalf of the US firm.
"Where's the evidence that Inc has the same board (as Ireland)?" Mr Hutley said.
"Where's the evidence Ireland operates under daily dictation?"
In fact the US firm was sometimes subcontracted by Ireland including to provide cookies served to Australian devices, he said.
"That does not involve carrying on business in Australia," he said.
The commissioner said Facebook.com's ownership, the service of cookies, the structure of Facebook Ireland and the reward of stock to Facebook Australia employees shows the US parent firm was involved in the collection and exposure of Australian users' private information.
"Once it is understood that is the website of Facebook Inc, the suggestion that Facebook Ireland alone is making that website available is untenable," barrister Ruth Higgins SC said.
"Facebook Ireland was an agent - in true common law sense - of Facebook Inc.
"Otherwise ... (the reference to) 'our' website really makes no sense. It was not Facebook Ireland's website, it was Facebook Inc's website."
Justice Tom Thawley will decide if the information commissioner has a prima facie case against Facebook Inc at a later date.