More than 1,200 church leaders have urged PM Boris Johnson not to introduce Covid vaccine certificates, saying they are an "unethical form of coercion".
In an open letter, the leaders - who include Anglican and Catholic ministers - warn passports could create a "surveillance state".
The government says it is reviewing whether to use vaccine certificates and "no decisions have been taken".
The UK equality watchdog says passports could create a "two-tier society".
Government ministers have said that certificates would allow people to show if they have been vaccinated, had a negative test or had natural immunity from a confirmed infection in the previous six months.
A government spokesperson said: "We are considering a range of evidence around Covid-status certification and whether it may have a role in opening up higher risk settings safely. The review is ongoing and no decisions have been taken."
As restrictions ease, certificates could play a role in reopening theatres, nightclubs and mass events like festivals, plus allow social distancing to be relaxed in hospitality venues.
But in the open letter to the prime minister, church leaders warned that introducing the passports would create a "medical apartheid".
"This scheme has the potential to bring about the end of liberal democracy as we know it and to create a surveillance state in which the government uses technology to control certain aspects of citizens' lives," the letter said.
"As such, this constitutes one of the most dangerous policy proposals ever to be made in the history of British politics."
The church leaders said that, regardless of the government's final decision, they would not refuse entry to their churches to anybody without a vaccine passport - or any other certificate which they have labelled "proof of health".
The open letter invited "leaders in churches of Christian organisations" from the UK to sign the letter, with copies going to the prime minister, leaders of the devolved governments and all MPs.
The government's suggestion of vaccine certificates has united MPs from all sides of the Commons, with No 10 facing criticism from those in both Conservative and opposition parties.
More than 70 MPs railed against the plan earlier this month, arguing that demanding medical proof in order to take part in local community life, such as going to the pub, was discriminatory and divisive.
Labour leader Sir Keir Starmer said he was "very worried" vaccine passports could lead to discrimination against people who have not received a jab.
And Tory MP Steve Baker labelled such certificates a "ghastly trap" that unfairly penalise those advised not to have a vaccine.