Brazil has prohibited the platform X, previously known as Twitter, from operating within its borders.
The ban was imposed because X failed to meet a deadline set by the Brazilian Supreme Court to appoint a new legal representative in the country.
Alexandre de Moraes directed the “immediate and total suspension” of the social media platform until it adheres to all court mandates and settles any outstanding fines.
The row began in April, with the judge ordering the suspension of dozens of X accounts for allegedly spreading disinformation.
Reacting to the decision, X owner Elon Musk said: “Free speech is the bedrock of democracy and an unelected pseudo-judge in Brazil is destroying it for political purposes.”
The social media platform is reportedly used by about 10% of Brazil’s 200 million residents.
By Saturday morning, some users had reported that they were unable to access the platform.
Earlier this month, the company closed its office in Brazil, citing threats of arrest against its representative if she did not follow what it called “censorship” orders, which the company deemed unlawful under Brazilian law.
Justice Moraes had decreed that X accounts involved in spreading disinformation, including many supporters of former right-wing president Jair Bolsonaro, must be blocked while under investigation.
He also stated that the company’s legal representatives would be held responsible if any accounts were reactivated.
X has faced threats of fines for not complying with this directive, with both the company and Mr. Musk accusing the judge of having a left-wing bias.
This situation adds to a series of conflicts involving the tech billionaire, who has had disputes with the EU over X’s regulation and recently engaged in a public disagreement with UK Prime Minister Sir Keir Starmer.
The head of Brazil’s telecommunications agency, responsible for suspending the platform, stated he is “proceeding with the compliance” to enforce the ban, according to Reuters.
Justice Moraes has set a five-day deadline for companies like Apple and Google to remove X from their app stores and block its use on iOS and Android devices.
He also warned that individuals or businesses using methods like VPNs to access the platform could face fines of R$50,000 (£6,700).
According to the judge’s ruling, the ban will remain in place until X appoints a new legal representative in Brazil and pays the fines for breaching Brazilian law.
In a previous update from one of its official accounts, X stated that it would not meet these demands.
“Soon, we expect Judge Alexandre de Moraes will order X to be shut down in Brazil – simply because we would not comply with his illegal orders to censor his political opponents,” the post said.
“The fundamental issue at stake here is that Judge de Moraes demands we break Brazil’s own laws. We simply won’t do that.”
Meanwhile, the bank accounts of Mr Musk’s satellite internet firm Starlink have been frozen in Brazil following an earlier order by the country’s Supreme Court.
Starlink responded with a post on X which said the “order is based on an unfounded determination that Starlink should be responsible for the fines levied – unconstitutionally – against X.”
Justice Moraes gained prominence after his decisions to restrict social media platforms in the country.
He is also investigating Mr Bolsonaro and his supporters for their roles in an alleged attempted coup on 8 January last year.
X is not the first social media company to come under pressure from authorities in Brazil.
Last year, Telegram was temporarily banned over its failure to cooperate with requests to block certain profiles.
Meta’s messaging service Whatsapp also faced temporary bans in 2015 and 2016 for refusing to comply with police requests for user data.