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 statement, Celtic admitted the fireworks were used, causing the referee to ask the club's safety officers to intervene and also revealed that 131 seats were damaged.
It read: "Three fireworks were exploded within Section 111, causing the referee to require a stadium announcement to be made instructing such behaviour to stop.
"As a result... Celtic FC will now be the subject of a disciplinary action for contravention of the UEFA Safety and Security Regulations."
Meanwhile, Norwich City look to have edged ahead of Queen's Park Rangers in the race to sign Gary Hooper after agreeing a fee believed to be £5m with Celtic for the striker.