Brazil blocked the social network X on Friday after its owner, Elon Musk, refused to comply with a Brazilian judge’s orders to suspend certain accounts, the biggest test yet of the billionaire’s efforts to transform the site into a digital town square where just about anything goes.

Alexandre de Moraes, a Brazilian Supreme Court justice, ordered internet providers to block access to X across the nation of 200 million because the company lacked a necessary legal representative in Brazil.

Mr. Musk closed X’s office in Brazil last week after Justice Moraes threatened arrests for ignoring his orders to remove X accounts that he said broke Brazilian laws.

X said on Thursday that it viewed Justice Moraes’ orders as illegal and that it planned to break their legal seal and publish them. “Unlike other social media and technology platforms, we will not comply in secret with illegal orders,” the company said in a statement.

In an unusual move, Justice Moraes also froze the finances of another Musk business in Brazil, SpaceX's Starlink satellite-internet service, to try to collect fines he has levied against X. Starlink — which has recently exploded in popularity in Brazil, with more than 250,000 customers — said that it planned to fight the order and would make its service free in Brazil if necessary.

Mr. Musk and Justice Moraes have been sparring for months. Mr. Musk says Justice Moraes is illegally censoring conservative voices. Justice Moraes says Mr. Musk is illegally obstructing his work to rid the Brazilian internet of hate speech and attacks on democracy.