Anyone age 12 and over attending the U.S. Open in person will now be required to show proof they've received at least one dose of the coronavirus vaccine. The mandate, announced Friday, reverses an earlier decision by organizers in which attendees did not need to be vaccinated or wear a mask if attending the tournament that starts next week.

The U.S. Tennis Association made the decision after the city extended its vaccination mandate for indoor venues to the Open. The event is held at the Billie Jean King National Tennis Center in Flushing, which is home to the Arthur Ashe Stadium, Louis Armstrong Stadium, and The Grandstand. Guests can show their physical vaccination card showing they have received at least one dose of the vaccine to enter the grounds. They can also show a photo of photocopy of their vaccination card or use the city and state vaccine apps to show proof.

In a statement posted on its website, organizers for the Open said they will be following COVID-19 guidelines mandated by the Centers for Disease Control and Prevention and city and state health officials. The decision, according to organizers, was intended to "ensure that we can provide our fans with the same world-class experience they've come to expect while ensuring a safe environment for all." A USTA spokesperson told the NY Post that unvaccinated fans can get a ticket refund, sell it to a vaccinated fan, or get at least one dose of the vaccine.

Last year the tournament took place in Queens without any fans in the stands. This year the tournament will be open to fans from August 30th through September 12th.

Mayor Bill de Blasio, who imposed the vaccination order, thanked the USTA for "putting the health and safety of New Yorkers first."

Initially, the USTA did not require the use of masks outdoors, proof of vaccinations, or a negative COVID test for guests to attend the Open in person. Organizers reportedly said the decision was made following CDC guidelines that only recommended masks, but not mandated them, for outdoor settings. Ticket-holders seeking autographs was also prohibited.

According to the New York Times, a doctor with the USTA's medical advisory board said the Open was initially given a green light to operate without any protocols by de Blasio and the city's health commissioner, Dr. Dave Chokshi. Spokespersons for the mayor's office or health department did not return an email seeking comment.

This didn't sit well with city and state lawmakers who found the decision reckless given the spread of the more contagious delta variant across the city. Queens was especially hit hard during the early months of the pandemic, and had initially been the epicenter of the outbreak.

"This needs to be fixed," New York City Councilmember Mark Levine, who chairs the council's health committee, wrote in a tweet before the decision was reversed.

A spokesperson for the USTA told THE CITY that "further evolution on what specifically qualifies as an indoor space became clear," and a reason for the organization to change their protocols. Arthur Ashe Stadium, for instance, has a retractable roof to protect players and guests from the elements.

The news pleased Queens state Senator Jessica Ramos, whose district in Queens was hard hit during the pandemic.

"Much better!" she wrote on Twitter.