Indian police used tear gas and water cannons on Friday to disperse opposition Congress party members during nationwide protests demanding the resignation of the head of the election commission, whom they accuse of manipulating voter rolls.

The “cockroach” youth movement, which counts millions of supporters and forced the education minister out in July, said it would launch protests across India on Oct 2 if Chief Election Commissioner Gyanesh Kumar does not resign by Saturday.

The protests, which are backed by other opposition groups, mark a new political challenge to Prime Minister Narendra Modi as Kumar, 62, a former civil servant, was appointed to head the independent Election Commission of India by Modi’s government.

“Theft of votes is happening across the country,” local Congress party leader Amarinder Singh Raja said in Chandigarh in the northwest, one of at least two places where police fired water cannon after protesters climbed buses and barricades.

Congress and other opposition parties have accused the eleciton commission of colluding with Modi’s Bharatiya Janata Party (BJP) to manipulate voter lists and win state elections in recent years, charges both the commission and the BJP have denied. Kumar himself has not commented.

Newspaper reports dissent within the commission

In at least a dozen of India’s 28 states, Congress supporters shouted slogans against Kumar, held up posters demanding his arrest and in one instance, burned an effigy of him and Modi.

In the capital Delhi, hundreds of protesters climbed barricades and hurled insults at a man wearing a Kumar mask.

The demonstrations were triggered by a report in the Indian Express newspaper on Wednesday that Kumar’s deputies had questioned him over changes to voter lists that opposition groups say benefit Modi’s BJP.

“For three years, I have been exposing vote theft. Now, the election commissioners themselves are acknowledging it and bringing the truth to light,” Congress leader Rahul Gandhi said late on Thursday, referring to Kumar’s deputies.

“Gyanesh Kumar has committed treason. He should resign immediately,” he added.

The Election Commission said differences among officers were normal in any institution and that all its actions were lawful. The BJP dismissed the report and said that opposition parties were indulging in a smear campaign because popular support for the BJP meant they lost elections.

State elections next year — including in the most populous state, Uttar Pradesh, and Modi’s home state of Gujarat, both ruled by the BJP — are key tests of support ahead of parliamentary elections due in 2029.