The Football Association urged fans to "respect the wishes" of England's players when they take the knee before Sunday's Euro 2020 clash with Croatia amid a simmering row over the gesture.
England start their European Championship challenge against Croatia at Wembley in a match that could be overshadowed by controversy over the kneeling issue.
Gareth Southgate's side were booed by a section of the crowd at Middlesbrough's Riverside Stadium when they kneeled in support of the Black Lives Matter movement before friendlies against Austria and Romania last week.
Premier League players have been taking the knee since last year following the death of George Floyd at the hands of a white police officer in the United States.
With 22,500 fans due at Wembley for the Croatia game, the possibility of more booing has been raised.
Southgate and British Prime Minister Boris Johnson have called on fans not to boo the gesture after England's players insisted they would carry on kneeling through the tournament.
Now the FA has underlined its stance and asked those with plans to boo the gesture to think about the negative image it would project.
"Tomorrow, our England senior men's team will begin their EURO 2020 campaign at our home, Wembley Stadium," an FA statement read on Saturday.
"Major tournaments don't come around often and when they do, it's an opportunity to unite friends, families and the country.
"As the team has reiterated many times, they will collectively take the knee ahead of their fixtures during the tournament.
"They are doing this as a mechanism of peacefully protesting against discrimination, injustice and inequality. This is personally important to the players and the values the team collectively represents."
The FA said England football had made it clear that it did not view the gesture "as being aligned to a political organisation or ideology".
"We encourage those that oppose this action to reflect on the message you are sending to the players you are supporting," the statement concluded.
Russia's players remained standing when their opponents Belgium all took the knee before Saturday's Group B match in Saint Petersburg.