The U.S. Soccer Federation's policy requiring its players to stand during the playing of the national anthem remains in place, while Major League Soccer says it would "respect and support" its players' choices.

The practice of kneeling for the national anthem, started last year by NFL quarterback Colin Kaepernick to protest racial inequality as well as police brutality in the U.S., has become more widespread in recent weeks.

It gained renewed momentum last weekend in the wake of comments by U.S. President Donald Trump, who called any NFL player who would kneel for the anthem a "son of a bitch," and said they should be "fired" by their respective teams.

But a spokesperson for U.S. Soccer told ESPN FC on Tuesday that nothing has changed with Policy 604-1, which it adopted in February.

The policy reads: "All persons representing a Federation national team shall stand respectfully during the playing of national anthems at any event in which the Federation is represented."

That protocol could be put to the test in the coming weeks. The U.S. men's national team will contest a pair of critical World Cup qualifiers in early October, while the women's side will play a pair of friendlies against South Korea later that month.

The USSF has been vague as to what the penalty would be for a player who is deemed to have violated the policy. The spokesperson indicated it would depend on how the player actually engaged in the protest.

Policy 604-1 was adopted in response to U.S. women's national team midfielder Megan Rapinoe, who knelt for the national anthem before a match against Thailand in a bid to show solidarity with then-San Francisco 49ers quarterback Kaepernick. Rapinoe did the same several times with her club, the Seattle Reign.

Rapinoe's protest drew a stern rebuke from the USSF, who in a statement last year said, "Representing your country is a privilege and honor for any player or coach that is associated with U.S. Soccer's National Team. Therefore, our national anthem has particular significance for U.S. Soccer.

"In front of national and often global audiences, the playing of our national anthem is an opportunity for our Men's and Women's National Team players and coaches to reflect upon the liberties and freedom we all appreciate in this country. "

As part of the privilege to represent your country, we have an expectation that our players and coaches will stand and honor our flag while the National Anthem is played."

Rapinoe responded by saying she would honor the USSF's policy, though prior to last weekend's NWSL league match between the Reign and FC Kansas City she opted to stay in the locker room along with teammates Lauren Barnes, Diana Matheson, Elli Reed and Madalyn Schiffel, as well as Kansas City players Becky Sauerbrunn, Sydney Leroux, Yael Averbuch and Desiree Scott.

MLS on Tuesday said it "encouraged" players to stand but will not require them to do so. No players have yet knelt before a league game.

"The march of players, officials and children into our stadiums and singing of the anthem has been a prematch tradition since our first game in 1996," the league in a statement. "The National Anthem provides our clubs and fans an important and time-honored opportunity to salute our country and stand up for its principles -- whether in the United States or in Canada.

"At the same time, freedom of speech -- and the right to peaceful protest -- are the hallmarks of both countries. Though we encourage our players to stand during the national anthem, we respect and support their right to express their personal beliefs."

The MLS Players Union released a statement on Monday defending the rights of players to "exercise their Constitutional rights."

"All players have every right to exercise their Constitutional rights and we will do everything in our power to defend those rights..." pic.twitter.com/piPlCfdi2R — MLS Players Union (@MLSPlayersUnion) September 25, 2017

MLS commissioner Don Garber sits on the USSF's board of directors, and was part of the discussion about the national federation's policy, for which he expressed his full support earlier this year.

"We felt very strongly that if you are given the honor of being called up to play for your country, and you're going to wear our flag on your chest, you should stand for the national anthem," Garber said at the time.

"And if you don't want to do that, you don't have to accept the call up, because there are dozens and dozens of other people who would probably enjoy that honor.

"We also followed kind of the guideline, if you will, sort of a referential indicator for us, was that if you're -- U.S. Soccer is a national governing body, it's under the auspices of the United States Olympic committee -- and if you are given the honor to represent your country with USA swimming, and you win a gold medal, you have to stand for the national anthem."