Celtic say their "sole motivation" is safety after warning supporters over several issues last week in the wake of a UEFA disciplinary charge over the use of fireworks at their Champions League clash with Cliftonville.
Fans will be offered the chance to relocate to another part of the ground or receive a refund on season tickets.
The supporters had earlier issued a statement describing the club's actions as "pathetic" and revealing they were seeking legal advice.
Celtic insisted their action came amid stated concerns from the Safety Advisory Group, which guides the city council on safety certificates, and their fears that the stadium could have its capacity cut or even be closed.
The club say concerns in the section include "overcrowding, moshing, body surfing, lateral movement and broken seating".
In a lengthy statement, Celtic said: "We trust that supporters will recognise that the club has been placed in an impossible position."
The statement continued: "It may seem to some that lateral movement is not unsafe.
"As noted above, that view is not shared by the Safety Advisory Group, or the club.
"The stadium is not designed for movement of that sort, leading to an increased risk of falling and injury.
"The movement led to seats being broken, which also presents a risk of injury.
"We are sure that supporters will agree that this behaviour is unsafe, particularly where there are young supporters in the area in question."
The Green Brigade, who have been the focal point for singing and displays at Parkhead in recent seasons, said in a statement on their website: "The Green Brigade are disappointed to announce that our section in 111 is to be closed by Celtic Football Club.
"Pathetically, this is due to 'lateral movement' which has been deemed 'unsafe' by the club's directors.
"Our group and section has continually made concessions and strived to be co-operative with the club over various safety concerns so we are left dismayed that such drastic and immediate action has been taken over such a trivial and harmless movement.
"The group is currently seeking legal advice and will consult with those in our section over the coming days."
The statement added: "We would like to stress that this is not the end of the Green Brigade.
"Decisions and hurdles like these will only strengthen our group's resolve."