The US government has indicated it does not support the implementation of a federal mandate that would require people who have been vaccinated against the coronavirus to carry a certificate.
White House Press Secretary Jen Psaki said on Tuesday that the government will not support a "system that requires Americans to carry a credential."
Psaki noted that a federal mandate requiring people to obtain a certificate could disadvantage those who choose not to be inoculated.
She said Americans' privacy and rights should be protected. She added that systems should not be used against people unfairly.
Debate is mounting in the United States over the introduction of vaccination certificates. Some states are adopting their own measures. The state of New York is already testing ways for people to present proof that they have been vaccinated.
Some countries, such as Israel, have adopted what are sometimes referred to as vaccine passports. The certificates must be presented at sports gyms and event venues.
The European Union is also considering the introduction of a proof-of-vaccination system.