Former Labour leader Jeremy Corbyn and senior Tory Iain Duncan Smith are among more than 70 MPs to launch a campaign opposing Covid passports in England.
Any demand to prove vaccination status to access jobs, businesses or services would be “divisive and discriminatory”, the cross-party group said.
It comes as the Daily Telegraph reported that a series of pilot tests for Covid passports were being planned.
The government said no final decision had been made on Covid certificates.
A review is taking place into whether such a system could help to reopen the economy in England, with discussions also taking place across the devolved nations.
‘Creeping authoritarianism’
Prime Minister Boris Johnson has previously said people could be asked to provide a vaccine certificate for entry into pubs in England, saying it “may be up to individual publicans”.
Certification could involve people being either vaccinated, having had a recent negative test or having previously been infected, the PM said.
Culture Secretary Oliver Dowden said vaccine passports could also be used as a “tool in the short term” to reopen theatres and sports stadiums.
But a broad coalition of MPs and peers have now signed a pledge saying they “oppose the divisive and discriminatory use of Covid status certification to deny individuals access to general services, businesses or jobs”.
The group contains some unlikely allies, with many of Mr Corbyn’s former shadow cabinet joining the lockdown-sceptic Covid Research Group of Conservative MPs in backing the campaign.
Accusing the government of “creeping authoritarianism”, Liberal Democrats leader Sir Ed Davey said: “As we start to get this virus properly under control we should start getting our freedoms back. Vaccine passports – essentially Covid ID cards – take us in the other direction.”
Sir Graham Brady, who chairs the 1922 Committee of backbench Tory MPs, added: “With high levels of vaccination protecting the vulnerable and making transmission less likely, we should aim to return to normal life, not to put permanent restrictions in place.”
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Privacy campaigning organisation Big Brother Watch also signed the pledge and published a report arguing against the measure.
The group’s director, Silkie Carlo, said: “We are in real danger of becoming a check-point society where anyone from bouncers to bosses could demand to see our papers. We cannot let this government create a two-tier nation of division, discrimination and injustice.”
In the campaign group’s report – entitled “Access Denied” – it said if certificates were brought it, in would be “the first policy for decades that could see segregation imposed throughout the population”.
Labour peer Baroness Chakrabati, another signatory of the pledge, said the report “paints a terrifying picture of what Britain might look like if internal Covid passports become part of our lives”.
She added: “They are a recipe for discrimination, bullying, corruption and public health buck-passing from government to individuals and businesses.
“Don’t tell us that that we lost so many loved ones only to surrender our liberties for good.”
The campaign comes after Labour leader Sir Keir Starmer this week said the use of Covid passports to decide whether people can enter pubs would go against the “British instinct”.
A government spokeswoman said: “The review is considering a range of issues, including the ethical, equalities, privacy, legal and operational aspects and what limits, if any, should be placed on organisations using certification.”
Meanwhile, the prime minister is to give an update on the Covid situation on Monday.
He is expected to confirm that data suggests the next stage of lockdown could ease in England on 12 April and that a traffic light system could be implemented for foreign travel, with countries being categorised as red, amber or green.
More than 31 million people have received the first dose of a coronavirus vaccine and more than 4.5 million have had a second dose, according to Thursday’s daily figures.
The figures also show there were a further 51 deaths within 28 days of a positive coronavirus test, bringing the total to 126,764. Some 4,479 new cases have been recorded.
