In recent days these worries have morphed into angry protests sparked by the passage of a new law giving non-Muslim migrants from Afghanistan, Pakistan and Bangladesh an easier path to citizenship.
“Five generations of mine have lived in this village and today I am being told that I am an infiltrator because I am a Muslim,” said Rehman, 50, recently released from internment in Assam in northeast India.
He was declared an alien in 2015 by a special tribunal as part of long-running efforts in Assam to root out outsiders, which culminated earlier this year with a state-wide register that the Modi government now wants to roll out nationwide.
“I have voted in many elections and have followed Indian laws all my life,” the father-of-four told AFP. “They are planning to banish us from our motherland.”
Assam’s register excluded 1.9 million people who now face possible statelessness, detention in camps or even deportation, although that is not feasible.
“They will be stateless and non-existent… and won’t have a say in the affairs of the government. They cannot do business, take jobs or get education or buy properties,” Abdul Kalam Azad, a local researcher told AFP.
“Those who cannot prove their Indian citizenship will either end up in detention centres or hide from authorities all their life.”
Decades of ethnic tensions and immigration from Bangladesh and West Bengal make Assam a case apart, as those excluded from the register are a mix of both Muslims and Hindus — the latter mostly Bengali speakers who Assamese fear will undermine their culture.
But elsewhere across India it is Muslims who fear they are Home Minister Amit Shah’s target when he says the national register will remove all “infiltrators” by 2024.
Modi says “genuine” Indians — the country’s 200 million Muslims included — have nothing to fear, but the experience in Assam of people left off the register suggests otherwise.
Inclusion required proof of residence in Assam before 1971 — something difficult in a poor state where many are illiterate of lack documentation.
The process was arbitrary and inconsistent.
In many cases one sibling made the cut and another didn’t, while some were left off due to a document typo or the whim of an overworked official.
These problems will likely be repeated when the register is done nationally — particularly among Muslims, who have India’s worst literacy rates, with 47 percent unable to read or write according to a 2011 census.
“People in Assam were prepared for the NRC and still 1.9 million were left out,” Azad said. “I can only imagine the fate of Indian Muslims in other parts of the country.”
‘Writing on the wall’
Outside of Assam, Muslims — as well as defenders of India’s secular tradition — are starting to panic, as seen in the current protests across the country of 1.3 billion people.
“The writing is on the wall. They want to build a Hindu nation along the lines of Israel… I feel as though this country is about to erupt,” Zubair Azmi, 46, a Muslim lawyer based in Mumbai told AFP.
“I know secular Hindus who are fighting at our side… but their numbers are falling because other Hindus are believing the BJP’s propaganda against Islam,” he said.
Ambreen Agha, a professor at the O.P. Jindal Global University in Sonipat, said the citizenship law follows other worrying events under Modi since he was re-elected in May.
In August New Delhi revoked the partial autonomy of Kashmir, India’s only Muslim-majority state.
In November the Supreme Court allowed a Hindu temple to be built in the flashpoint town of Ayodhya where Hindu zealots demolished a mosque in 1992.
Modi’s first term also saw a rise in lynchings of Muslims over cows — sacred to many Hindus — and other hate crimes, activists say. Many Muslim-sounding towns and cities were re-named.
But the citizenship law, which Modi insists is not anti-Muslim, has acted as the final straw.
“It happened first with the Kashmir issue. At that time we kept quiet… Then came the (Ayodhya) verdict,” said Ayesha Renna, a Muslim woman who made headlines this week for protecting a fellow student from baton-wielding police in Delhi.
“Next they will be targeting the whole of India,” she told a TV channel.
Professor Agha suggested opposition to the law would only grow.
“There were resistances in the past, but what is happening today on the streets is unprecedented in the history of modern India,” she told AFP.
“They have nothing to lose now.”