Millions of women and homeless people will be barred from voting in elections because of biases and difficulties in getting identification papers, human rights groups said on Tuesday, warning this would increase their marginalisation.
Every citizen who is 18 years or older has a right to vote in polls due to start on April 11, with about 900 million citizens eligible to take part.
But the country's homeless population, who mostly live in cities and are estimated to number more than 4 million by human rights groups, are likely to be denied this right despite efforts by authorities to get them registered.
The Delhi Election Commission, whose motto is "no voter left behind", accepts night shelters, street-lights and flyovers as temporary residences.
This enabled more than 10,000 homeless people in the capital New Delhi to receive voter identity cards in 2014, ahead of the last general election, said Ashok Pandey of Shahari Adhikar Manch, an advocacy group.
But since then only another 3,000 homeless people have been signed up.
"If they are not at the given address when they do the verification, their name is cancelled. That's a problem because they keep moving," he told the Thomson Reuters Foundation.
"It really should not matter that they are homeless - they are still citizens and have a right to vote," he said.
The Delhi government is trying to reach all homeless people through non-profits working with them, said Bipin Rai, an official at the Delhi Urban Shelter Improvement Board.
"We have helped process thousands of voter ID forms. But there are also hundreds of voter IDs lying unclaimed," he said.
A spokeswoman for the Election Commission did not respond to emails and calls seeking comment.
Having a voter identity card can also help homeless people get other documents, enabling them to open bank accounts and access welfare benefits, said Shivani Chaudhry, executive director of advocacy Housing and Land Rights Network.
"A voter ID gives them an identity, and being able to vote gives them some dignity. Otherwise, they are invisible," she said.
"But the card says 'homeless', which brands them, and makes them feel more marginalised."
Also missing from India's voter rolls are women, who are often barred from voting - or told whom to vote for - in many families, according to election analysts Prannoy Roy and Dorab Sopariwala.
As many as 21 million women are not on voter lists, the cumulative effect of non-registration over decades, they write in "The Verdict", a book on India's elections, an extract of which was published in Outlook magazine.
"It is a result of a combination of social and political factors. What is worrying is that it is worsening over time."