India’s opposition parties protested in New Delhi Monday, calling for the rollback of a controversial revision of the voter list in one of the country’s poorest states, where key elections are scheduled in November.

Critics warn it could lead to voter disenfranchisement.

Hundreds of lawmakers and their supporters began the protest from India's Parliament and were confronted by police, who stopped them from marching towards the election commission office in, New Delhi.

Police briefly detained some lawmakers, including opposition leader Rahul Gandhi. 

The opposition accuses the Election Commission of India of rushing through a huge electoral roll revision in eastern Bihar state, saying the exercise could render vast numbers of citizens unable to vote.

The revision of nearly 80 million voters involves strict documentation requirements from citizens. There are concerns it could lead to the exclusion of vulnerable groups, especially those who are unable to produce the paperwork required to prove their citizenship.

Some of the documents required include birth certificates, passports and matriculation records. Critics and opposition leaders say they are hard to come by in Bihar, where the literacy rate is among the lowest in India.

They say the exercise will impact minorities the most, including Muslims, and keep them from voting.

India does not have a unique national identity card. The widely used biometric-linked identity card called “Aadhaar” is not among the documents listed by the poll body as acceptable proof for the electoral roll revision.

The election body has denied the allegations and said it has ensured no eligible voter is “left behind." It has also said the “intensive revision” is a routine update to ensure the accuracy of electoral rolls and needed to avoid the “inclusion of the names of foreign illegal immigrants." 

According to the poll body, some 49.6 million voters whose names were included in a similar exercise in 2003 are not required to submit any further documents. But that still leaves almost 30 million other voters potentially vulnerable.

A similar revision of voters is scheduled to be replicated across the nation of 1.4 billion people.

Bihar is a crucial election battleground state where Prime Minister Narendra Modi’s ruling Hindu nationalist Bharatiya Janata Party has only ever governed in a coalition.

Poll results there could likely impact the balance of power in India's parliament where Modi's government relies on coalition partners, including a regional party from Bihar.

AP video shot by Piyush Nagpal