The Lions of Teranga were cruelly knocked out of Russia 2018, despite having the same number of points and goal difference as their Asian counterparts.
And while they were aware of the ruling prior to the 1-0 defeat to Colombia and head coach Aliou Cisse took the exit with grace - the tactical change of the Japanese in the final 10 minutes of their defeat to Poland has come under major scrutiny.
"The federation believes that Japan literally refused to play when it learned that Colombia had just scored a goal against Senegal, a refusal to play that suited Japan but which is contrary to the principles governing football," the letter stated, as quoted by the BBC.
"The federation is all the more shocked that the Japan coach did not deny the facts. In the post-match press conference, the latter even confirmed he had made the decision to manipulate the result by keeping the score at 1-0."
"The Senegalese Football Federation deplores the lack of fair play this Japanese team has shown. It challenges Fifa on the notion of ranking the number of cards which loses its meaning and interest when the team lacking fair play is not worried by any penalty."