The arrest of 22-year-old climate activist Disha Ravi has sparked widespread outrage, with many calling it an attack on free speech.
She was arrested on Saturday over a shared document to help farmers protest against new agricultural laws.
Delhi Chief Minister Arvind Kejriwal described her arrest as an "unprecedented attack on democracy".
Several activists and journalists have also been arrested in recent weeks in connection with the protests.
Now in their third month, the protests have come to represent one of the biggest challenges faced by prime minister Narendra Modi's Bharatiya Janata Party (BJP) government.
Police said Ms Ravi was a "key conspirator" in the "formulation and dissemination" of the document - a protest "toolkit".
They said Ms Ravi, one of the founders of the Indian branch of the Fridays for Future climate strike, was an editor of the document and had shared it with Swedish climate activist Greta Thunberg.
"I did not make the toolkit. We wanted to support the farmers. I edited two lines on 3 February," Ms Ravi told the court, according to the NDTV news site.
Mr Kejriwal has joined several prominent voices online, including activists, journalists and opposition politicians (such as former finance minister P Chidambaram), all of whom appear both shocked and furious over the arrest.
Arrest of 21 yr old Disha Ravi is an unprecedented attack on Democracy. Supporting our farmers is not a crime.— Arvind Kejriwal (@ArvindKejriwal) February 15, 2021
The Indian state must be standing on very shaky foundations if Disha Ravi, a 22 year old student of Mount Carmel college and a climate activist, has become a threat to the nation— P. Chidambaram (@PChidambaram_IN) February 14, 2021
Ok now we're arresting 21-year old climate activists. Well done India, you big superpower you— Mihir Sharma (@mihirssharma) February 14, 2021
Ms Ravi, who lives in the southern city of Bangalore, was flown to the capital Delhi where she appeared before a magistrate on Sunday. She was sent to judicial custody for five days.
Questions have been raised over the fact that Ms Ravi did not have a lawyer during her hearing - a fact which criminal lawyer Rebecca John, who has been tracking the case, described as "a shocking abdication of judicial duties" in a Facebook post.
"If the accused was not being represented by counsel at the time of the hearing, the magistrate should have waited till her counsel arrived or in the alternate, provided her with legal aid," Ms John wrote.
It's unclear still what Ms Ravi is being charged with, but many fear she is being held under a colonial-era sedition law that has been used in recent arrests against journalists.
People charged under the draconian law have to surrender their passports, are not eligible for government jobs and must produce themselves in the court as and when required.
The Delhi police, who arrested Ms Ravi, invoked the same law earlier this month when they said they were investigating the toolkit. They said it suggested a conspiracy in the run up to a huge rally on 26 January, which saw protesting farmers clash with police.
The toolkit was hugely publicised about two weeks ago when Ms Thunberg tweeted it, voicing her support for protesting farmers.
The farmers are seeking the repeal of new agriculture reform laws that will further open up India's farming sector to corporate buyers and investment.
The government, which has offered to suspend the laws, says they will improve farming incomes. But farmers, who want nothing short of a complete withdrawal, say the opposite will happen. They fear the laws will threaten decades-old concessions guaranteed by the government and leave them vulnerable to the private market.
Ms Ravi's arrest is being seen by many as an intimidation tactic by the federal government, which oversees the Delhi police.
DishaRavi's arrest is the latest escalation in India’s crackdown on free expression&political dissent as it seeks2stifle the farmers’ mass protests, says the @dailytelegraph UK. Doesn’t GoI care about the damage it’s doing to its own global image? https://t.co/TILH9XKYkg— Shashi Tharoor (@ShashiTharoor) February 14, 2021
If arresting a 21 year old environmental activist for sharing a social media tool kit is not a sign that we have descended into police state territory, I don't know what is ?— T M Krishna (@tmkrishna) February 14, 2021
And the intention is also to threaten young people of this country#DishaRavi
"This is a new low, even for India," environmentalist Nityanand Jayaraman told the BBC. "These are the kinds of young people we should be celebrating, and not jailing."
He described her as "conscientious, outspoken youngster who has constantly defended and fought for India's rights on the global stage" on the issue of climate change.
He said this runs contrary to PM Modi's efforts to enlist youth in cleaning up cities as part of his flagship Swachh Bharat (Clean India) Campaign
My Jayaraman added that it sent a clear message to young people that "they should restrict themselves to picking up garbage on the streets or planting trees, and not come into the arena of policy-making".
Farmers' group Samyukta Kisan Morcha, one of the main groups behind the protests, expressed their support for Ms Ravi and demanded her release.
Support has poured in from everywhere, including Indian film actor Siddharth, Canadian poet Rupi Kaur and US Vice President Kamala Harris's niece Meena Harris.
we demand india #freedisharavi. we demand they #freenodeepkaur and all the other women in jail w her. we demand they #freeshivkumar & the hundreds of innocent farmers they’ve illegally arrested for practicing their democratic right to protest.— rupi kaur (@rupikaur_) February 14, 2021
enough is enough.
Indian officials have arrested another young female activist, 21 yo Disha Ravi, because she posted a social media toolkit on how to support the farmers' protest. Read this thread about the sequence of events and ask why activists are being targeted and silenced by the government. https://t.co/ycUgDEqwdF— Meena Harris (@meenaharris) February 14, 2021