Koum, a Facebook board member, wrote on the social media site, "I have always admired Tim Cook for his stance on privacy and Apple's efforts to protect user data. … We must not allow this dangerous precedent to be set. Today our freedom and our liberty is at stake."
And Edward Snowden, who first criticized Pichai for not immediately speaking out, proceeded to retweet the Google CEO.
Many tech experts also supported Apple's decision, with one telling CNBC that Cook's decision to stand by customers' privacy is correct.
"His priority is to provide privacy to [Apple] customers," said Tim Bajarin, president of Creative Strategies, an advisory firm that provides market research services for the technology industry.
"If [Cook] gave the FBI the 'back door' encryption code, it would set a precedent," Bajarin told CNBC.
"It is true that [the government] is positioning this as an isolated case, but because of the way our justice system works, it becomes a precedent, and once a precedent is set, [the government] or other cases can come back and use this to try and get the same action in the future" he said.
Bajarin adds that if Apple sets the precedent for U.S. government to access the iPhone contents via "brute force," Russia and China could follow suit and try to use similar rulings to access information.
In a country that has a longstanding tradition of granting its citizens civil liberties, the "American public opinion is split," said Edward Reilly, global chief executive officer of strategic communications at FTI Consulting.
"When people think there is a legitimate issue of national security, [then the] government can have enhanced authority, but they're very uncomfortable with that," said Reilly.
With the passage of the Patriot Act post-Sept. 11, how the law enforcement and intelligence community used their extended authorities to access private information has been hotly debated.
The issue of privacy versus national security is not a new topic, but Cook's refusal to comply with the court order is.
"I think this is an important enough issue that the Supreme Court should decide," said John Mauldin, chairman of Mauldin Economics.
Modern society also has "to decide how much privacy we want, how we want to legislate it, and how we want to control it," Mauldin said in a CNBC interview.