It’s Boris Johnson’s latest coronavirus battle.
The prime minister, having spent the autumn and winter facing attacks from Conservative lockdown sceptics about his COVID restrictions, is now facing a fight against those same MPs over potential plans to introduce “vaccine passports”.
This time, though, Johnson is now facing defeat as Labour – which supported his lockdown measures – is voicing scepticism about the measure.
Here, Yahoo News UK takes you through who is opposing the so-called vaccine passports and when a vote could take place.
Why is the government considering vaccine passports?
Johnson is planning to lift all restrictions on social contact in England on 21 June at the earliest, though it has been widely acknowledged ending lockdown will result in a COVID-19 infection spike.
England’s chief medical officer Professor Chris Whitty last month also warned the next wave of cases will still cause a “significant number” of deaths later this year.
As a result, vaccine passports are seen as a way for people to prove their COVID status before going to events in order to reduce the need for social distancing.
Watch: What is the UK's future on testing, travel and vaccine passports?
A government review into “COVID status certification” found they could “potentially play a role” in settings such as theatres, nightclubs and mass events.
The certificates would include vaccination status, test results or evidence of someone having contracted and recovered from COVID.
Predictably, though, a row is brewing over their use, with Johnson himself acknowledging on Monday there are "ethical and practical issues" surrounding vaccine passports.
Who is opposing vaccine passports?
Johnson is facing a battle against at least 40 Conservative MPs who oppose the plans, including rebels who campaigned against the winter lockdown restrictions such as 1922 Committee chair Sir Graham Brady and COVID Recovery Group chair Mark Harper. Harper said vaccine passports “will lead to a two-tier Britain”.
These Tory MPs have formed an unlikely coalition with the likes of former Labour leader Jeremy Corbyn who, along with many of his former shadow cabinet members, also oppose the plans.
On Friday, this coalition of more than 70 MPs launched a campaign against against the “divisive and discriminatory” scheme.
And, adding to Johnson’s problems, there are increasing signs Labour leader Sir Keir Starmer will oppose them.
Starmer has previously raised doubts over vaccine passports, and while he has not yet set out an official position, his shadow health secretary, Jonathan Ashworth, told BBC Breakfast on Tuesday the party is “very sceptical”.
Asked if he would vote against any form of domestic COVID passport, Ashworth said: “We don’t think asking you to produce a vaccination passport, which is this digital ID card, is fair. It’s discriminatory.”
Meanwhile, civil rights campaign groups such as Big Brother Watch, Liberty, the Joint Council for the Welfare of Immigrants (JCWI) and Privacy International have also set out their opposition to vaccine passports.
When will MPs vote on vaccine passports – and could Boris Johnson lose?
On Tuesday, vaccines minister Nadhim Zahawi confirmed MPs will be able to vote on the use of vaccine passports should the government decide to roll them out.
So, with a final decision on that yet to be made, it's not known when a vote will take place.
But, given the 21 June target date for lifting lockdown, we can assume a vote would be held well ahead of this date given Johnson's acknowledgement of the "practical issues" implementing such a scheme.
One thing is for sure, though – Johnson is facing defeat if Labour decides to oppose vaccine passports.
Even if Labour does support the scheme, a vote as it stands would be hairy for the government, given the 70-odd MPs across all parties who currently oppose it. According to the Institute of Government, Johnson’s working majority is 87.
Therefore, if Johnson does decide to go ahead with vaccine passports, he will need to find a way of appeasing at least some of his Tory “passport sceptics” – or risk an embarrassing defeat at the House of Commons vote.
Watch: How England is leaving lockdown