Maria Ressa, a high-profile Philippine journalist and vocal critic of the country's president, was arrested Wednesday in connection with "cyber libel" charges against Rappler, the news site she oversees.

Ressa, who is Rappler's CEO, confirmed that she was served an arrest warrant in a phone call with CNN. She was formally arrested later on Wednesday, according to JJ Disini, one of her lawyers.

The award-winning journalist was served an arrest warrant by Philippines National Bureau of Investigation (NBI) officers.

Ressa told reporters shortly after receiving the warrant that the fact it had been issued was "interesting," adding that she was "shocked that the rule of law has been broken to the point that I can't see it."

U.S. Senator Brian Schatz responded to the recent arrest, saying that Ressa should be freed, and that journalists should not be 'silenced.'

"These charges should immediately be dropped, and Ms. Ressa should be free to go about her work," said Schatz. "Instead of trying to silence journalists who are accurately reporting the news, the Filipino government should focus on protecting democracy and defending the country’s constitution, including its commitment to a free press."

Rappler said the charges are over an article it published in 2012. However, the cyber libel law only came into effect in the Philippines in 2014. The NBI ruled in January that because the report preceded the law, Ressa could not be charged. But that judgment was over-turned by the Department of Justice on the grounds that the news article was updated in February 2014.

Francis Lim, a lawyer collaborating on the case, said in a statement to CNN that it was "a sad night for the rule of law and press freedom in the Philippines."

"It means that the law can be twisted by the powers as a weapon against journalists who expose their wrongdoing to the public," Lim said. "This case was originally dismissed for lack of merit and resurrected within days and decided against Ressa in an effort to silence the press. We trust that our courts of law will come to the rescue of our ideals that are held sacred by our Constitution."

Hawaii's U.S. Senator also says the American government to step up and condemn the arrest.

“I also call on the U.S. government to condemn this arrest, and stop giving cover to strongmen who want to erode press freedom,” Schatz said.