The debate unfolding around the world over coronavirus vaccine mandates is playing out on a small scale at United Nations headquarters ahead of a meeting of dozens of world leaders in New York next week.

New York City officials have requested that heads of states, and the many diplomats traveling with them, show proof that they are fully vaccinated before entering the U.N. hall for the annual opening of the General Assembly, one of the top diplomatic events of the year.

The request got the backing of the General Assembly’s president, Maldivian Foreign Minister Abdulla Shahid. In a statement released on Wednesday, New York Mayor Bill DeBlasio and International Affairs Commissioner Penny Abeywardena thanked U.N. diplomats for working with them on the issue, calling them “true New Yorkers” for helping the city recover.

But not all those diplomats professed the same camaraderie. In a letter to colleagues released on Wednesday, Russian U.N. Ambassador Vasily Nebenzya called the requirements “a clearly discriminatory measure” and said that they were a violation of the U.N. charter.

This Russian opposition to the vaccine requirement prompted harsh words from DeBlasio on Thursday, with the New York mayor telling reporters that “if the Russian ambassador is against it, I’m for it” and suggesting that the Russians had “invalidated themselves” by trying to disrupt U.S. elections.

The Russian Mission to the United Nations did not respond to a request for comment.

The news comes amid broader tensions: Experiments with coronavirus mandates in Europe, the United States and elsewhere have created friction as variants spread — and as countries struggle to balance public health restrictions with individual liberties.

New York has started requiring proof of at least one coronavirus shot to allow people into restaurants, gyms, movie theaters and other indoor venues.

But for foreign diplomats, there is a further complication: Countries administer different coronavirus vaccines — including ones that have not been granted emergency use authorization in the United States.

Sputnik V, a vaccine backed by Moscow and widely administered in Russia, does not have approval in the United States and is not on the World Health Organization’s emergency use listing either.

New York officials have announced that they will give out free doses of the single-shot Johnson & Johnson vaccine by the U.N. headquarters in Midtown, but it is not approved in all U.N. member states either, though it does have WHO emergency use listing.

Speaking on Thursday, DeBlasio brushed aside these concerns, suggesting that anyone with a “nonapproved” vaccine could get vaccinated again in New York. Speaking of the Russian diplomats, DeBlasio said, “if their vaccine isn’t good enough, then they should go and use one of the other vaccines."

Despite DeBlasio’s comments, officials from both New York City and the U.N. admitted on Thursday that the details about a vaccine mandate were still up in the air. Some U.N. officials bristled at the idea that city officials could infringe upon the U.N.'s carefully crafted extraterritoriality status.

New York officials were "looking forward to seeing how the UN will implement this policy,” Abeywardena, in charge of the city’s international affairs, said in a statement on Thursday.

Stéphane Dujarric, a spokesman for U.N. Secretary General António Guterres, suggested that the United Nations had previously deployed an “honor system” when it came to vaccines and testing for the novel coronavirus, and that they were working with the “sitting President of the General Assembly to continue that honor system in a way that is acceptable for all.”

By the understanding of the United Nations, “the letter from NY City authorities does not specify any vaccine,” Monica Villela Grayley, a spokeswoman for the General Assembly president, wrote in an email.

The pandemic meant that no delegations went to New York last year for what turned into a virtual annual gathering. Next week, however, more than a hundred heads of state, including President Biden and Turkish leader Recep Tayyip Erdogan, plan to attend in person, while others will give video speeches.

Guterres, speaking to Reuters this week, said he expects that most of the officials flying to New York are immunized, but the dispute has also highlighted drastic inequality: While the United States plans to initially offer certain groups of people booster shots, only 2 percent of the world’s 5.7 billion administered doses have reached people in Africa.

This report has been updated.