FIFA has opened disciplinary proceedings against England and Scotland for wearing poppies during last Friday's World Cup qualifier
The two countries stood shoulder to shoulder in defiance of a governing body rule at Wembley, wearing black armands with the remembrance poppy in honour of Armistice Day.
FA chief executive Martin Glenn warned FIFA they would fight any possible punishment ahead of the fixture and insisted their legal case was "rock solid".
But on Thursday, FIFA announced: "We can confirm disciplinary proceedings have been opened on this matter.
"Please understand we cannot comment further at this stage nor speculate on any outcome or provide an estimated timeline."
After a week of confusion over whether wearing the symbol would amount to breaking FIFA's Law Four, the 22 players in white and pink stood for a minute's silence in memory of members of the armed forces who have lost their lives.
The match-day programme also featured the poppy on the cover and the flower was shown on the Wembley screens, as FA chairman Greg Clarke and SFA president Alan McRae stood on the touchline alongside senior representatives from the British Army, Navy and RAF moments before kick-off.
After both country's national anthems were respectfully observed, the 'Last Post' trumpet melody echoed around Wembley during the moment's silence and, behind the Wembley goals, England fans wore red and white t-shirts, bearing the poppy, to form the St George's Cross.
Writing in a special match-day programme, FA chairman Clarke said: "We will of course be marking the Royal British Legion's Poppy Appeal at tonight's fixture.
"We welcome those serving soldiers we have invited as part of ongoing support for the Tickets for Troops cause and I would also like to pay tribute to the work of the Commonwealth War Groves Commission, and their Living Memory
campaign.
"At the FA, and on Armistice Day, we feel it entirely appropriate that we join with the nation, our fans in the stadium and those watching on TV to commemorate those made the ultimate sacrifice. We will remember them."