Tens of thousands of demonstrators are expected to gather in New Delhi on Sunday to protest against Prime Minister Narendra Modi. The Indian National Congress organized this rally over voter roll changes. Mohammed Shamin said, "B.J.P., Modi -- all are trying to demolish our rights, our constitution." Many people will attend.

Organizers are calling for one of the biggest demonstrations yet, in a string of rallies that has racked India since the summer.

Tens of thousands of demonstrators are expected to converge on India's capital on Sunday in a display of mass resistance to the government of Prime Minister Narendra Modi and recent changes to the voter roll.

The event, organized by India's largest opposition political party, the Indian National Congress, will be the latest in a string of large protests to ripple through New Delhi since this summer.

The demonstrators have marched under different banners, with separate leaders and demands. But they have all expressed unhappiness with Mr. Modi's nationalist Bharatiya Janata Party, which has led India since 2014, and its initiative to update India's voter rolls. The protesters have accused Mr. Modi of "vote theft," claiming that his party is using its powers to try to rig the rolls in its favor.

"B.J.P., Modi -- all are trying to demolish our rights, our constitution," said Mohammed Shamin, 40, a private tutor from Delhi who planned to attend. As he mingled among the several hundred people who had started to gather at the demonstration site in central New Delhi on Saturday evening, Mr. Shamin said he was optimistic that their presence would make a difference.

"Every cloud has a silver lining," he added, gesturing to the early arrivals and the large empty field behind them that organizers expected would be crammed by morning with people from all over India.

Organizers have said they expect as many as a million people to attend, but police officials have provided a much lower estimate of 50,000. Laborers worked through the night on Saturday to prepare the open-air venue, which was still waterlogged from heavy rain earlier in the week.

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