Celtic have admitted that they are 'extremely disappointed' that the club have been hit with a fine in the region of £42,000 after a group of fans displayed "illicit" banners against AC Milan in the Champions League.
Bhoys supporters unfurled a banner showing images of IRA hunger striker Bobby Sands and Scottish nationalist William Wallace, along with song lyrics that included the line, 'the terrorist or the dreamer?'.
The European governing body decided to take action as rules state that banners of a political and ideological nature cannot be displayed in a stadium.
A statement from Celtic said: "Clearly it is extremely disappointing that the club must pay another sizable penalty following the actions of a small minority, particularly given the previous assurances which were made to the club and the widespread understanding of the likely outcome of such actions.
"Regrettably, due to previous charges being brought against the club, again following the actions of a small minority, the fines imposed by UEFA are increasing in scale.
"It goes without saying that such actions must stop now, before the club receives a competitive sanction or one which would affect our supporters attending European matches."
Celtic supporters group the Green Brigade were behind the banners.