BRASILIA, April 7 (Reuters) - A standoff between Elon

Musk and Brazil escalated on Sunday when a Supreme Court judge

opened an inquiry into the billionaire after Musk said he would

reactivate accounts on the social media platform X that the

judge had ordered blocked.

Musk, the owner of X and a self-declared free speech

absolutist, has challenged a decision by Justice Alexandre de

Moraes ordering the blocking of certain accounts. He has said X,

formerly known as Twitter, would lift all the restrictions

because they were unconstitutional and called on Moraes to

resign.

Neither Musk, X nor Brazilian authorities have disclosed

which social media accounts were ordered blocked. X first posted

about the order to block on Saturday but it was not immediately

clear when the order was issued.

Moraes is investigating "digital militias" that have been

accused of spreading fake news and hate messages during the

government of former far-right President Jair Bolsonaro and is

also leading an investigation into an alleged coup attempt by

Bolsonaro.

Musk said in an X post on Saturday evening accused Moraes of

"brazenly and repeatedly" betraying the constitution and people

of Brazil.

"This judge has applied massive fines, threatened to arrest

our employees and cut off access to X in Brazil," he said in the

post.

"As a result, we will probably lose all revenue in Brazil

and have to shut down our office there. But principles matter

more than profit."

The billionaire had pledged to legally challenge the order

blocking X accounts where possible.

Moraes responded on Sunday by adding Musk to the

investigation he is leading into fake news on social media, and

opening an inquiry into what he called an obstruction of

justice.

In his decision, Moraes said: "X shall refrain from

disobeying any court order already issued, including performing

any profile reactivation that has been blocked by this Supreme

Court."

If X fails to comply with the order to block certain

accounts the company will be fined 100,000 reais ($19,740) per

day, the judge said in a statement released to media.

President Luiz Inacio Lula da Silva's leftist government

expressed support for Moraes, with Solicitor General Jorge

Messias criticizing Musk and calling for the regulation of

social media networks to prevent foreign platforms from

violating Brazilian laws.

"We cannot live in a society in which billionaires domiciled

abroad have control of social networks and put themselves in a

position to violate the rule of law, failing to comply with

court orders and threatening our authorities," Messias said in a

post on X.

Last year, Moraes also ordered an investigation into

executives at social messaging platform Telegram and Alphabet's

Google, who were in charge of a campaign criticizing a

proposed internet regulation bill.

The bill put the onus on internet companies, search engines

and social messaging services to find and report illegal

material, instead of leaving it to the courts. It would also

impose hefty fines for failures to do so.