West Bengal Chief Minister Mamata Banerjee called yesterday's action a "disturbing trend" while her Kerala counterpart, Pinarayi Vijayan, said it sought to "threaten" a critical media.
Congress leader Ghulam Nabi Azad said the raids reflected "shamelessness".
He said, "Yesterday, we were seeing shamelessness. While people have vanished with thousands of crores (of rupees), why is the government so rattled by a Rs-50 crore matter?"
Banerjee tweeted she was "shocked" at the raids. "He (Roy) is highly respected and reputed. Disturbing trend," she said.
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Calling it a "serious matter", the CPI said the action reflected the Narendra Modi government's plan to curb the freedom of expression.
"The party expresses its deep concern over the raids...A part of the Modi government's plan to curb freedom of expression," it said in a statement.
A number of media bodies also condemned the raids.
"While we maintain that all individuals and every institution have to abide by the law of the land, we condemn any attempt to either intimidate the media or put curbs on its freedom," PCI president Gautam Lahiri said.
The Indian Women's Press Corps (IWPC) here alleged that the law of the land should not be applied "selectively", nor should it be "used as an instrument to harass anyone including the media".
A group of intellectuals under the banner of SAHMAT, a platform for artistes, academics and others, condemned the raids as "totally unwarranted" and said they were an "intimidatory" tactic.
"By attacking the media, the present government is undermining the freedom of the press, so essential for a democratic polity," it said.
In the Himachal Pradesh capital of Shimla, citizens expressed their solidarity with NDTV at a protest in front of a statue of Mahatama Gandhi at the Ridge.
The protesters, who gathered under the banner of Citizens of Shimla, were led by CPI(M) leaders Sanjay Chauhan and Tikender Singh Panwar.
The CBI converted a private complaint against the NDTV into an FIR and carried out searches on the premises of its founders Prannoy Roy and Radhika Roy, and their company RRPR Pvt Limited, yesterday.
NDTV in a statement said the channel and its promoters would fight tirelessly against this "witch-hunt" by multiple agencies.
"We will not succumb to these attempts to blatantly undermine democracy and free speech in India. We have one message to those who are trying to destroy the institutions of India and everything it stands for: we will fight for our country and overcome these forces," the NDTV said.