Documents could include a record of whether someone has had a vaccine and if they were recently tested for the virus.
However, the former Brexit Secretary said on Tuesday: “The impact of this would be discriminatory. Under the law, it would be indirectly discriminatory and that is illegal.
“You may well find, it has been said, that black and ethnic minority communities are less inclined to get vaccinated, well that would be indirect discrimination.”
Younger people were also less likely to have the jab and “some people have ethical or religious objections”, he told the Public Administration and Constitutional Affairs Committee.
He said the Government must put any plans for such passports to full parliamentary scrutiny, adding: “If we do this it should be primary legislation because it is so serious.”
However, Mr Davis did accept there was a potential case for international vaccine passports, telling the committee: “I am in favour of an international vaccine passport, that seems to me to be perfectly reasonable because the balance of advantage heavily favours that and the intrusion on the individual’s liberty is much lower.”