The document indicates that players, coaches, and trainers must stand for both the U.S. and Canadian national anthems and "do not have the discretion to waive" the rule. Violators can be penalized by the league office.
In the memo, deputy commissioner Mark Tatum also offered alternative means of addressing the protest movement that's become prevalent in the NFL and other leagues. He suggested players and coaches spread a message of unity through a joint pregame address or video tribute.
The memo aligns with commissioner Adam Silver's message, as he said Thursday he expects players to stand for national anthems.
NFL quarterback Colin Kaepernick started the movement last season when he began kneeing during the national anthem to protest racial injustice and police brutality. He's since been exiled from the league, but his message lives on, with players, coaches, and owners showing solidarity last weekend.
Over in The Association, many NBA players have spoken out against President Trump, including superstars LeBron James, Stephen Curry, and Kevin Durant. The latter two, as well as the rest of the defending champion Golden State Warriors, won't visit the White House after Trump withdrew their invitation over Curry's hesitation to attend.
Team owners have been less vocal as to not alienate pro-Trump fans, sources told ESPN. NBPA executive director Michele Roberts has encouraged players to discuss issues that matter to them, and said the union is prepared to respond if the league disciplines players for protesting.