Keir Starmer has blasted a "jabs for jobs" policy amid mounting claims bosses could demand staff are vaccinated against coronavirus before returning to offices.
Transport Secretary Grant Shapps warned that firms could require employees to be inoculated so they can go back to workplaces.
"We are not going to make that legislation, that every adult has to be double vaccinated before they go back to the office – but yes, it is a good idea and yes, some companies will require it,” he said.
"It's a reality that for some companies, they will say, 'We need our staff now to be double vaccinated'.”
But Labour leader Mr Starmer hit back: "I don't agree with that.
"I can see a case for vaccine passports, alongside testing, when it comes to big sporting events or mass events, certainly for international travel.
"But for day-to-day routine – access to the office, access to health services or dentistry or even food – I don't agree with vaccine passports for day-to-day access."
Foreign Secretary Dominic Raab has backed firms requiring staff to be double-jabbed.
He said this week: "I can understand why employers think that that would be a smart policy or approach to encourage, whether or not there should be hard and fast legal rules."
The Lib Dems stepped up their demand for MPs to cut short their summer breaks to debate a tweak to the NHS app which allows people to use Covid passes in England.
Party leader Sir Ed Davey wrote to Boris Johnson saying: “It is deeply unsettling to see you and your Government committing to vaccine passports by stealth.
“It is time to step up, to own your decision on Covid ID cards and put it to a vote to Parliament. You must recall Parliament now."
