Some churches in and around India’s financial capital Mumbai have begun asking worshippers to give a declaration in writing – “I came here to pray of my own free will.”

Visitors write down their names, sometimes add an ID card number, and sign to say that nobody forced or enticed them to attend church. The forms, a copy of which the BBC has seen, have no official standing. Churches keep them in case a prayer meeting is challenged and its organisers are accused of trying to convert those inside.

The practice began at some churches in late August, just before a new law against religious conversion took effect in Maharashtra state, of which Mumbai is the capital.

The law prohibits religious conversions brought about by force, fraud, coercion or inducement. It also requires people who want to convert voluntarily to notify authorities in advance. An unlawful conversion can lead to a prison sentence of up to seven years, rising to 10 for a repeat offence.

Maharashtra’s government says the law protects people, particularly those who are socially or economically vulnerable, from being forced or deceived into changing their religion.

But critics say its broad definitions, severe penalties and scrutiny of even voluntary conversions risk drawing the state and the police into one of the most private decisions a person can make. The state government did not respond to the BBC’s repeated requests for comment.

While the law applies to all religions, the anxiety is being felt most deeply at places where minorities, especially Christians, worship. At the heart of the debate is a long-running tension over allegations, usually made by right-wing groups, about people being coerced or induced to change their religion for benefits.

Devdan Tribhuvan has seen some of that anxiety up close.

A fourth-generation Christian in Vasai, a suburb of Mumbai, he is part of an organisation that provides legal aid to Christians in and around the city. In recent months, he says, people have increasingly approached him not about court cases, but with accounts of disrupted prayer meetings and questions about what they are still free to do.

Some have described strangers walking into churches and questioning those inside: “What is your name? Why are you here? Has anyone offered you something?”