Videos released by opposition leaders show that several senior figures were detained in New Delhi on Saturday.
They include Arvind Kejriwal, leader of the Aam Aadmi Party and former chief minister of Delhi.
“It’s official… we are living under an absolute dictatorship,” Kejriwal wrote on X.
Mamata Banerjee, who lost power as West Bengal’s chief minister earlier this year, was also detained.
Pinarayi Vijayan, a communist leader who headed the southern state of Kerala until May, was among those detained.
Rahul Gandhi, leader of India’s opposition Congress party, called the crackdown an act of “cowardice” and described Prime Minister Narendra Modi, Home Minister Amit Shah, right-wing, Hindu nationalist RSS chief Mohan Bhagwat, Chief Election Commissioner Gyanesh Kumar and National Security Adviser Ajit Doval as “the villains of this story” who were “slowly finding the space closing around them. We are closing that space.”
Priyanka Gandhi Vadra, Rahul Gandhi’s sister and a Congress MP, wrote in a social media post: “India is not a democracy anymore. It is a dictatorship being run by Mr. Narendra Modi and Mr. Amit Shah.”
Opposition parties and critics have warned that the electoral-roll revision exercise could strip millions of people of their voting rights and give an advantage to Prime Minister Modi’s ruling Bharatiya Janata Party (BJP).
The Election Commission of India has rejected allegations of wrongdoing, saying the “special intensive revision” aims to remove duplicate and ineligible voters.
The protests echo the CJP’s mass mobilization in July, which forced the then education minister to resign over an examination scandal.
This time, demonstrators are demanding the resignation of election chief Gyanesh Kumar.
