The governing body punished the Polish side due to racist behaviour from the club's supporters in a Europa League match at Lokeren in November 27.
Referee Michael Koukoulakis was forced to halt the game so that an announcement could be made to the visiting contingent warning them to refrain from racist behaviour.
Legia, whose fans also set off fireworks and launched objects, subsequently lodged an appeal, but UEFA has upheld its original ruling.
The club are also banned from selling tickets to supporters for their next away Europa League tie, while a fine of €105,000 has been imposed.
It is not the first time the Warsaw outfit have found themselves in hot water with UEFA.
They were fined over an anti-UEFA banner displayed during a Europa League clash with Aktobe, with fans objecting to the governing body's decison to throw the club out of the UEFA Champions League for fielding an ineligible player against Celtic.
Legia were also been fined over crowd disturbances at Metalist Kharkiv.
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