The U.S. Soccer Federation has adopted a policy that says national team players "shall stand respectfully" during national anthems.
The policy was approved last month but came to light Saturday before the U.S. women's national team lost to England in a SheBelieves Cup match. A Fox Soccer analyst posted an image of the rule on Twitter.
The policy comes after midfielder Megan Rapinoe knelt during the anthem at a pair of national team matches last year. Rapinoe has said she wanted to express solidarity with San Francisco 49ers quarterback Colin Kaepernick, who knelt last season in an attempt to bring attention to racial inequality.
Rapinoe was not on the roster for the national team for the SheBelieves Cup tournament while she continues to regain her form after knee surgery. She also knelt last year during a game with the Seattle Reign, her National Women's Soccer League team.