Veterans groups are divided about the propriety of NFL players sitting during the national anthem when they take the field on the opening Sunday of the football season, which takes place on the 15th anniversary of the Sept. 11, 2001 terrorist attacks.

San Francisco 49ers quarterback Colin Kaepernick began the practice of sitting during the national anthem during the NFL preseason, as a way of protesting apparent cases of police brutality. The protest sparked controversy inside the league and out of it, but some players decided to join Kaepernick’s protest. The Miami Dolphins held a players-only meeting to discuss a possible demonstration, and the Seattle Seahawks announced that they also intend to make a statement.