A regional court in Sao Bernardo do Campo ordered Brazil's telecom operators to block WhatsApp from 0200 UTC Thursday as punishment for the company's refusal to cooperate with an investigation.
WhatsApp co-founder and CEO Jan Koum took to Facebook to criticize the move.
"We are disappointed in the short-sighted decision to cut off access to WhatsApp, a communication tool that so many Brazilians have come to depend on, and sad to see Brazil isolate itself from the rest of the world," Koum wrote.
Brazil's telephone operators have long complained that the application's offer of free voice calls over the Internet cuts into their business.
But the temporary block is apparently due to an impasse over WhatsApp's cooperation in assisting with a criminal investigation, the court said in a statement.
BandNews TV: App favored by crime lords
Brazil's private BandNews cable TV channel reported that the case revolves around a suspected drug trafficker linked to the notorious First Command of the Capital (PCC) gang, one of the largest criminal syndicates in Sao Paolo.
The trafficker allegedly used WhatsApp services in the commission of crimes, the channel reported without revealing its source.
The US-based company acquired by Facebook is used by millions of people in Brazil, the world's fifth most populous country. Worldwide, it has around 900 million monthly active users.
jar/sms (Reuters, AFP, EFE)