Anatel commissioner Artur Coimbra told Reuters that the regulator is inspecting all Brazilian telecom operators to make sure they have shut down the X social media platform as ordered by a Supreme Court justice.
Starlink is the only company that has told Anatel it will not comply with the ruling by Judge Alexandre de Moraes, Coimbra said in an interview.
Starlink is a unit of Musk-led rocket company SpaceX.
Earlier, a Supreme Court panel voted unanimously to uphold the suspension of X in the country for defying a court order, blocking access to more than 20 million users.
Moraes last week ruled that X should be suspended in Brazil because it did not name a local legal representative as required by law and a prior court order that set a deadline for compliance.
Justices Flavio Dino, Cristiano Zanin, Carmen Lucia and Luiz Fux sided with Justice Alexandre de Moraes.
Three of the justices on the panel said the suspension could be reversed if the platform complied with previous rulings.
X was taken down in Brazil in the early hours of Saturday following Moraes' decision.
Brazil is X's sixth-biggest market globally with about 21.5 million users as of April, according to Statista.
Moraes also ordered that those who continued to access X via VPNs be fined up to 50,000 reais ($A13,000) per day.
Moraes and X owner Elon Musk have been locked in a months-long feud after the social media platform challenged orders to block accounts accused by investigators of spreading misinformation and hate.
Musk has argued that Moraes sought to censor users and closed the X office in Brazil in August without appointing a new representative, triggering the suspension.
On Monday, Musk replied, "Exactly," to a post that described the suspension as an attack on freedom of expression and Brazilians' rights.
Siding with Moraes, Justice Dino wrote, "It is not possible for a company to operate in the territory of a country and intend to impose its vision on which rules should be valid or applied."
Dino, Zanin and Fux nonetheless indicated that they would be open to reconsidering the decision if X complied with court rulings.
Chief Justice Luis Roberto Barroso, who was not on the review panel, said that removing legal representatives to avoid complying with court decisions "is a behaviour that would not be acceptable anywhere in the world".
X remained inaccessible for most users in Brazil.
Starlink said it was refusing to remove X from its service until a freeze on its Brazilian bank accounts was lifted.
Moraes last week froze Starlink's accounts after X did not pay fines imposed for failing to turn over documents.
