Indian women use their smartphones while traveling in the New Delhi metro car reserved for women. (Anna Zieminski/AFP/Getty Images)

When a bridge collapsed in the city of Kolkata, killing dozens two months ago, the usual outrage followed about shoddy construction companies and substandard material.

But a wealthy businessman, Motilal Oswal, created a stir on Twitter when he chose to blame it on the country’s engineers — who he said graduate not because of talent but because of affirmative-action set-asides for lower-caste groups, a hot-button issue in India.

He was retweeted by hundreds of people opposed to set-asides, but faced a strong pushback on Twitter from the Dalits, once known as the “untouchables” in India’s centuries-old rigid caste system.

Within hours, Oswal deleted the tweet and apologized.

Much like the “Black Twitter” movement in the United States, Dalits with popular Twitter handles are now routinely flexing their muscles on the microblogging site, acting as community watchdogs and highlighting issues of bias, brutality and bigotry that they say India’s predominantly upper-caste media tends to ignore.

Dalits launched an angry counterattack on Oswal on Twitter with the hashtag #BoycottMotilalOswal and asked followers to file a complaint of caste prejudice. They also pointed out that the company that was building the bridge did not have job quotas for lower-caste engineers, and that set-asides in colleges and government jobs are a fundamental right guaranteed by the nation’s constitution.

They widely shared screen shots of Oswal’s offending tweet and of his apology.

“Twitter has given a new language and energy to the Dalit movement against the caste system in India,” said Pradeep, who runs the Ambedkar Caravan Twitter handle. He uses only one name because surnames in India often reveal one’s caste.

India’s lower-caste groups have been marginalized for centuries. The majority of Dalits toil as landless farm laborers, cannot use community water pumps, live in segregated village enclaves and work as manual scavengers. The marriage of an upper-caste member to a Dalit is largely frowned upon, and can even be fatal in some villages. Many Dalits are too poor to own smartphones or access the Internet.

But more than six decades of affirmative-action policies has created a small but vocal Dalit middle class composed of bureaucrats, doctors, politicians and engineers.

Recently, Dalits on Twitter forced a big Indian company that makes ceiling fans to remove a TV commercial that they said showed affirmative action in a poor light. The ad celebrated a lower-caste student who refuses the benefits of affirmative action in college.

“For upper-caste people, Twitter is just another invention. For Dalits, it has the potential for a revolution,” said Chandra Bhan Prasad, a Dalit writer. “There is no barrier for Dalits’ entry here. Nobody will filter your words here or chop your thumb for daring to write what you feel.”

Although Dalits have preferred Facebook for activism for some years, their attention shifted to Twitter when the site enabled the use of hashtags in six more regional Indian languages last year.

A little more than 22 million Indians used Twitter in 2014, according to one report, but many say it is growing in its power to shape public debate. Many politicians, including Prime Minister Narendra Modi, tweet regularly. Political parties have huge Twitter armies to propagate their views or troll opponents. Communities also use it to influence or criticize the stories that the mainstream media covers.

Yet the Indian media remains largely an upper-caste bastion with no formal affirmative- action policy to hire Dalits, say media experts, one reason that “Dalit Twitter” has found its niche.

“The national media has no active interest in covering Dalit issues on a regular basis,” said Dharma Teja, of the Twitter handle Dalit Camera.

In March, the body of a 17-year-old Dalit student was found inside the water tank of her college dorm in the western state of Rajasthan. Her parents said she had been raped and killed by the college physical training instructor, but the college said it was suicide. As protests grew on the ground, the national television networks were consumed by the suicide of a TV soap-opera actress instead.

“By amplifying the voices of Dalit protests on the ground, we forced the national media to pay more attention to the student’s case,” Teja said.

During a recent campus face-off between Dalit students and university administrators in the southern city of Hyderabad, sparked by the suicide of a Dalit PhD student, these Twitter handles actively posted videos, photographs and oral testimonies.

Journalists in New Delhi said they used these handles as a key source of information on the protest.

When there is a violent incident, many like the Dalit politician D. Ravikumar use the hashtag #DalitLivesMatter.

Some, however, say they do not use Twitter merely to highlight violence.

“Ask anybody in India who the top 10 Dalit women in history were, they would struggle to name even two. That is how total the erasure of our history has been,” said Thenmozhi Soundararajan, whose handle is Dalit Diva. She uses #DalitHistoryMonth and #DalitWomenFight in many of her tweets. “We are trying to liberate our history.”

Things may be beginning to change.

Last month, a news portal called became the first mainstream English media outlet in India to run a Dalit History Month series on caste discrimination, Dalit poetry and art.

Dhanya Rajendran, editor in chief of the portal, said such stories do not find much space in the media because “there is an assumption that the audience is upper-caste and urban.”

Readers accused the portal of dividing society along caste lines by running the series.

One reader commented: “What is Dalit history? Don’t take up old prejudices for publicity. New India not like that.”

Dalits on Twitter said they face a volley of abuse and rampage trolling.

“This shows that it’s working,” Soundararajan said. “They are scared of the rising power of Dalit Twitter.”