The Polish champions defeated Celtic 2-0 at Murrayfield in the second leg of their third qualifying round tie last week, sealing a 6-1 aggregate success.
However, the late introduction of defender Bartosz Bereszynski has caused controversy, with Legia believing the player to have previously served a three-match suspension.
UEFA disagree, claiming that Bereszynski was not registered for Legia's second-round tie with St Patrick's and his suspension was therefore not fulfilled.
The governing body subsequently awarded Celtic a 3-0 win, enough to see them progress to the play-off round on away goals.
Coach Henning Berg announced Legia's intention to appeal the decision on Friday, and on Tuesday UEFA announced that the club had followed through with that process.
"Legia Warszawa have appealed against the decision taken by the UEFA Control, Ethics and Disciplinary Body on August 8," a UEFA statement read.
"The meeting of the UEFA Appeals Body will be held on Wednesday August 13."
