WhatsApp has been blocked in Brazil for 48 hours. 

A judge ordered phone companies to impose the temporary shutdown, which began at 9 p.m. ET Wednesday, because WhatsApp failed to respond to a court order in a criminal case.

The Facebook-owned app has more than 100 million Brazilian users. "This is a sad day for Brazil," Facebook chief Mark Zuckerberg wrote in an online post. "Until today, Brazil has been an ally in creating an open Internet."

Citing local news station Band News TV, Reuters reported that the case in question involves a drug trafficker linked to the Primeiro Comando da Capital (PCC)—the country's largest criminal organization—who allegedly used WhatsApp to carry out his crimes.

"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," WhatsApp CEO Jan Koum wrote in a Facebook post.

According to the São Paulo State Justice Tribunal in São Bernardo do Campo, the company failed to comply with a judicial order issued on July 23. The court then hit WhatsApp with a fine for non-compliance on Aug. 7.

"I am stunned that our efforts to protect people's data would result in such an extreme decision by a single judge to punish every person in Brazil who uses WhatsApp," Zuckerberg said.

Facebook is "working hard to get this block reversed," according to Zuckerberg, who reminded users that Facebook Messenger "is still active."

WhatsApp's loss is Telegram's gain, though. The app, which recently tangled with WhatsApp, has seen a spike in sign-ups since WhatsApp went dark.

1.500.000 and counting, SMS-Gateways overloading. Hang on, your codes are coming! We've got all hands on deck to accommodate the crazy load. — Telegram Messenger (@telegram) December 17, 2015

The news comes as GOP presidential frontrunner Donald Trump argued that he would be open to closing off some "areas" of the Internet if it could help combat terrorism.