The platform's Global Government Affairs team on Saturday said Australia's eSafety Commissioner had ordered it to remove posts that commented on the attack.
But they said the posts did not violate X's rules on violent speech.
The team claimed the regulator demanded X "globally withhold these posts or face a daily fine of $785,000".
"X believes that eSafety's order was not within the scope of Australian law and we complied with the directive pending a legal challenge," the Global Government Affairs team posted on Saturday.
"While X respects the right of a country to enforce its laws within its jurisdiction, the eSafety Commissioner does not have the authority to dictate what content X's users can see globally.
"We will robustly challenge this unlawful and dangerous approach in court."
The recent attacks in Australia are a horrific assault on free society. Our condolences go out to those who have been affected, and we stand with the Australian people in calling for those responsible to be brought to justice. — Global Government Affairs (@GlobalAffairs) Following these events, the Australian eSafety…April 19, 2024
The commissioner has only said it was considering whether further regulatory action was warranted, after it put social media platforms on notice to remove graphic content showing recent violence in Sydney.
Calls have grown for harsher sanctions for social media platforms in the wake of the April 13 shopping centre massacre at Bondi after distressing footage of the attack was uploaded online and misinformation spread.
"We will take the necessary steps to ensure compliance with these notices," the watchdog said in a statement on Friday.
"In relation to X Corp, eSafety is working to ensure the company's full and complete compliance with Australian law."
NSW Premier Chris Minns blasted X on Saturday and said it was about time penalties for social media companies were strengthened.
"This is exactly as I'd expect from X, or Twitter, or whatever you want to call it - a disregard for the information that they pump into our communities, lies and rumours spreading like wildfire," Mr Minns told reporters.
"Then when things go wrong, throwing their hands up in the air to say that they're not prepared to do anything about it."
Bishop Mar Mari Emmanuel was allegedly stabbed during a church sermon. (HANDOUT/Christ of Good Shepherd Church)
A 16-year-old boy was charged over the church stabbing, and on Friday evening, a 45-year-old man was arrested at a Fairfield Heights home and charged with rioting and threatening violence, causing fear.
The man was refused bail to appear in Parramatta Bail Court on Saturday.
Police hope high-visibility patrols in the region will curb conflict after the knife-wielding teenager allegedly struck Bishop Mar Mari Emmanuel, 53, who was delivering a sermon on Monday night.
The stabbing - which has since been declared an act of terrorism - triggered a riot outside the Christ the Good Shepherd Church in Wakeley leaving dozens of police officers injured.
Australian Federal Police Commissioner Reece Kershaw said investigators believed the attack met the criteria of a terrorist act, but he refused to go into further detail.
The stabbing triggered a riot outside the Christ the Good Shepherd Church in Wakeley. (Bianca De Marchi/AAP PHOTOS)
The lawyer of the boy charged over the stabbing told a court the teenager had received intermittent treatment for his mental health for years.
Muslim, Christian and Jewish groups have issued statements calling for calm.
The Jewish Council of Australia, the Islamophobia Register Australia, and the Columban Centre for Christian-Muslim Relations warned against the spread of misinformation.
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