Celtic have put the Green Brigade on a final warning after UEFA opened an investigation into the "setting off of fireworks" at Tuesday night's home Champions League second qualifier against Cliftonville.
The Parkhead club have an uneasy relationship with the 'Ultras' group housed in section 111 of the stadium and now claim their behaviour is putting the club's General Safety Certificate at risk.
In a strongly-worded statement on the club's website, Celtic admitted the fireworks were used, causing referee Thorsten Kinhofer to ask the club's safety officers to intervene and also revealed that 131 seats were damaged.
The statement read: "Three fireworks were exploded within Section 111, causing the Match Referee to require a stadium announcement to be made instructing such behaviour to stop.
"As a result of this unprecedented step by a match official, Celtic FC will now be the subject of a disciplinary action for contravention of the UEFA Safety and Security Regulations."
The statement reminded supporters that "the club has been under close scrutiny by the Glasgow City Council Safety Advisory Group with regard to serious safety concerns within section 111".
To that end, it also admitted that several safety concerns, including: Overcrowding of section 111 resulting in unsafe congestion: The refusal of spectators to comply with the direction of safety stewards: The unsafe lateral movement of spectators blocking aisles: 'Moshing' - mock fighting/jostling - causing crowd disruption and damage to seating and the 'body surfing' of young people over the heads of spectators, were all "evident" during the 2-0 win over the Irish part-timers.
Only discussions between the club's supporters' liaison officer and representatives of the Green Brigade prevented section 111 being closed but the club will monitor the situation at both the Celtic versus Borussia Monchengladbach match on Saturday and the first leg of their third qualifier against Swedish side Elfsborg at Celtic Park next Wednesday night.
The statement continued: "The club is keen to work with spectators in section 111 to resolve safety concerns.
"However, it should be understood that failure to stop this unsafe behaviour will require the closure of this area in Celtic Park.
"The club recognises the many examples of good support for the team emanating from this part of the ground and in particular the efforts of the 'Green Brigade' in organising positive displays which are commended.
"However, the unsafe aspects of spectator behaviour in section 111 require to be addressed with immediate effect.
"The directors and board of Celtic Football Club consider their responsibilities with regard to spectator safety to be of paramount importance.
"We will continue dialogue with representatives of fans in this area to resolve these serious safety concerns, however this unsafe behaviour must stop."
Celtic have to answer a charge which allegedly breaches articles 16.2 of UEFA's disciplinary regulations.
Article 16.2 decrees that "all associations and clubs are liable for....inappropriate behaviour on the part of their supporters and may be subject to disciplinary measures and directives even if they can prove the absence of any negligence in relation to the organisation of the match" relating to, among other things, the "lighting of fireworks or any other objects".
Celtic were fined 25,000 euros (approx £21,000) for fans' misbehaviour in the Europa League game against Udinese in Italy in December, 2011.
After the 1-1 draw at the Stadio Friuli, the Parkhead club were charged with "the displaying of a banner of an offensive nature and the setting off of fireworks by supporters".