For N.B.A. referees, agreeing to a vaccine mandate, a rarity in U.S. sports, was ‘not that difficult.’

Late last month, the N.B.A. sent out a short news release announcing an agreement with the union representing the league’s referees to mandate Covid-19 vaccines. It stipulated that all referees must to be fully vaccinated to work games, including “recommended boosters.”

The agreement stands out in the sports world, where Covid vaccinations remain largely a point of contention. And it is unusual even for pro basketball itself: No such mandate exists with N.B.A. players, creating a potentially awkward situation where some league employees are mandated to take the vaccine and others aren’t.

Marc Davis, the union’s president and a referee himself for more than two decades, said in an interview that the agreement was born of a strong relationship with the N.B.A., and that the referees were broadly in favor of the mandate.

“When you have a collaborative environment between management and labor, I think you’re constantly always working through issues and there’s a constant dialogue back and forth,” Davis said.

“It’s a shared view of vaccines that they are probably one of the top three inventions in the history of humankind. And to have this access to this innovative vaccine and allow us to continue to work, to do our business and to continue to work collaboratively, it’s not that difficult of a conversation to begin and to work through.”