ELON Musk accused Apple Inc of threatening to block Twitter Inc from its app store without saying why in a series of tweets on Monday that also said the iPhone maker had stopped advertising on the social media platform.

The billionaire CEO of Twitter and Tesla said Apple was pressuring Twitter over content moderation demands.

The action, unconfirmed by Apple, would not be unusual as the company has routinely enforced its rules and previously removed apps such as Gab and Parler.

Parler, which is popular with U.S. conservatives, was restored by Apple in 2021 after the app updated its content and moderation practices, the companies said at the time.

"Apple has mostly stopped advertising on Twitter. Do they hate free speech in America?," Musk, who took Twitter private for $44 billion last month, said in a tweet.

He later tagged Apple Chief Executive Officer Tim Cook's Twitter account in another tweet, asking "what's going on here?"

Apple did not immediately respond to requests for comment.

"It wasn't clear to me how far up the Apple food chain that idea went internally and without knowing that, it isn't clear how seriously to take any of this," said Randal Picker, a professor at the University of Chicago Law School.

The world's most valuable firm spent an estimated $131,600 on Twitter ads between Nov. 10 and Nov. 16, down from $220,800 between Oct. 16 and Oct. 22, the week before Musk closed the Twitter deal, according to ad measurement firm Pathmatics.

In the first quarter of 2022, Apple was the top advertiser on Twitter, spending $48 million and accounting for more than 4% of total revenue for the period, the Washington Post reported, citing an internal Twitter document.

Twitter did not immediately respond to a Reuters request for comment on the report.

'GO TO WAR'

Among the list of grievances tweeted by Musk was the up to 30% fee Apple charges software developers for in-app purchases, with Musk posting a meme suggesting he was willing to "go to war" with Apple rather than paying the commission.

The fee has drawn criticism and lawsuits from companies such as Epic Games, the maker of 'Fortnite', while attracting the scrutiny of regulators globally.

The commission could weigh on Musk's attempts to boost subscription revenue at Twitter, in part to make up for the exodus of advertisers over content moderation concerns.

Companies from General Mills Inc to luxury automaker Audi of America have stopped or paused advertising on Twitter since the acquisition, and Musk said earlier this month that the company had seen a "massive" drop in revenue.

Ad sales account for about 90% of Twitter's revenue.

The self-described free speech absolutist, whose company has in the past few days reinstated several Twitter accounts including that of former U.S. President Donald Trump, has blamed activist groups for pressuring advertisers.

Ben Bajarin, the head of consumer technologies at research firm Creative Strategies, said that Musk may be reading too much into a regular process Apple goes through in app review.

"App review from Apple is not perfect by any means and a consistently frustrating process for developers but from what I hear it is a two-way conversation," he said.