Scottish champions Celtic have issued a final warning to a section of their support after UEFA opened an investigation into the "setting off of fireworks" at Tuesday's Champions League qualifier.
The Hoops hierarchy have an uneasy relationship with a group dubbed the 'Green Brigades' who sit in section 111 of Parkhead Stadium and now claim their behaviour is putting the club's General Safety Certificate at risk following a series of firework explosions during the Cliftonville clash.
The referee was forced to call for stewards to take action after fireworks were let off during the second leg victory over Northern Irish part-timers Cliftonville.
And 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".
Celtic were fined Â£21,000 for their fans' misbehaviour in the Europa League game against Udinese in Italy in December 2011.
After the 1-1 draw at the Stadio Friuli, Celtic were charged with "the displaying of a banner of an offensive nature and the setting off of fireworks by supporters".
"The club is keen to work with spectators in section 111 to resolve safety concerns," the Celtic statement continued.
"However, it should be understood that failure to stop this unsafe behaviour will require the closure of this area."