The rice farmer doesn’t know how it happened. Abdul Mannan just knows a mistake was made somewhere. But what can you say when the authorities suddenly insist one of your five children isn’t an Indian? What do you do when your wife and daughter-in-law are suddenly viewed as illegal immigrants?

“We are genuine Indians. We are not foreigners,” said Mannan, 50, adding his family has lived in India’s northeastern Assam state since the 1930s. “I can’t understand where the mistake is.”

Neither can nearly 4 million other people who insist they are Indian but who now must prove their nationality as the politics of citizenship — overlaid with questions of religion, ethnicity and illegal immigration — swirls in a state where such questions have a long and bloody past.

Today, nativist anger churns through the hills and plains of Assam state, just across the border from Bangladesh, with many here believing the state is overrun with illegal migrants.

“India is for Indians. Assam is for Indians,” said Sammujjal Bhattachariya, a top official with the All Assam Students Union, which has been in the forefront of pushing for the citizenship survey. “Assam is not for illegal Bangladeshis.”

“We need a permanent solution,” he added.

On Friday, some of the 3.9 million residents left off Assam’s draft list of citizens began picking up forms to file their appeals, wading into a byzantine legal and bureaucratic process that many fear could lead to detention, expulsion or years in limbo.

Mannan, his two daughters and two of his sons were all listed on the citizenship list released in July. But his wife, a 17-year-old son and his daughter-in-law were nowhere to be seen. No explanation was given.

“We are worried that the names are not there,” said Mannan, who lives with his family in a bamboo-walled hut, supporting them on about $150 a month in farming income. “How will we live? What will we do? How will we stay in Assam?”

For decades, fears of widespread movement across the porous border with Bangladesh have triggered tensions between the state’s majority ethnic group, Assamese-speaking Hindus, and its Bengali-speaking Muslims.

Read: Fear grips Assam as four million made stateless

In the 1980s that erupted into violence, with hundreds of people killed in Assam amid waves of anti-migrant attacks. New Delhi eventually ruled that anyone who could prove their family had lived in India before Bangladesh’s 1971 war of independence, which drove millions of Bangladeshis to flee across the border, would be considered an Indian citizen.

But proving that can be deeply complicated in a region where basic paperwork — birth certificates, marriage certificates, leases — has only recently become commonplace in many rural villages.

State officials insist they have done everything possible to make the procedure fair.

“It’s been an extremely exhaustive process,” said Prateek Hajela, the coordinator of the citizenship project that involves 52,000 officials, visits to 6.8 million families and countless hearings to examine the details of family trees.

But the politics of religion and ethnicity have been on the rise in India since 2014, when the Hindu nationalist Bharatiya Janata Party was swept to power in national elections. The party quickly pushed to update the citizenship registry in Assam, where politicians have eagerly grabbed hold of the issue.

“First our target is to segregate the foreigners. What steps we will take against them will come next,” Assam’s top elected official, Sarbananda Sonowal, told the Times of India in an interview early this year. “They will have only one right — human rights as guaranteed by the UN that include food, shelter and clothing.”

“For almost 40 years our people have been living in a state of confusion and uncertainty,” he told the newspaper.

Uncertain status

Today, hundreds of Bengali-speaking Muslims with suspect nationality are already living in a half-dozen detention camps in Assam.

Assam has a population of roughly 33 million, with a little over one-third of them Muslims.

“The concern over illegal migration is indeed genuine,” said Akhil Ranjan Dutta, a political analyst and professor at Gauhati University in Assam. “But unfortunately, political parties have always tried to score brownie points on the issue purely to gain votes.”

Few deny there has been widespread illegal migration into Assam, often by poor Bangladeshis in search of work as farm laborers. The state’s demographics have shifted dramatically in recent decades, with the percentage of Bengali-speakers jumping from 22 percent in 1991 to 29 percent in 2011, and the percentage of Assamese-speakers declining. Many analysts, however, say those numbers in part reflect the higher birth rates among Muslims. Estimates on the number of illegal immigrants vary wildly, from a few hundred thousand to many millions.

While Muslims appear to dominate the 3.9 million people left off the citizenship rolls, they aren’t the only people now facing a bureaucratic gauntlet.

“I don’t know about politics. I am a poor man. I work all day, eat, and sleep at night. I don’t go anywhere else,” said Khitish Namo Das, 50, a rail-thin Hindu farmer who insists he was born in India and whose family of eight — except for one daughter-in-law — are now considered illegal.

“When the names did not appear on the list it made me worry,” he said, then reassured himself: “I have the documents so I don’t think I need to worry too much.”

It’s not clear what will happen to people who, once their appeals are used up, are still not listed as citizens. Detention is a strong possibility for some, but impoverished Bangladesh insists it will not accept mass expulsions back into its territory. Activists worry many could be left in limbo for years, perhaps decades, stateless wanderers like Myanmar’s Rohingya Muslims.

Even some of those who support the citizenship survey say the migrants are a significant part of the economy.

“Those immigrants play a very important role in supplying your labor economy. So if those people are given work permits, minus political rights, they could be very valuable in Assam,” said Nani Gopal Mahanta, an Assam-based political analyst.

But he defends the survey: “It’s a question of sovereignty, it’s a question of the security of this country.”

Officials insist that the process will be open and trustworthy.

“It’s going to be a fair procedure,” Hajela, the project coordinator, said last week. “We will ensure that no genuine citizen gets left out, and at the point in time, ensuring that the ineligibles don’t find their names there.”