Tennison Road bridge is to shut completely for nine months from June due to ongoing upgrades.
The bridge, in South Norwood, will be closed until Network Rail completes work to strengthen it and widen its structure.
Croydon Council said the bridge had been scheduled to shut in August, following periods of temporary closure from June.
But Network Rail and the council said they decided to bring forward the permanent closure "avoid confusion".
Councillor Wayne Lawlor predicted the closure would cause "bedlam" and criticised the lack of consultation on the changed plan.
He said: "It has been done very much under the radar without any thought or consideration to the local community at all.
"The congestion is going to be unbearable. It's going to have really seriously impact. What are they trying to do, kill off South Norwood?"
Coun Lawlor called on the council to offer compensation packages to local businesses affected by the closure.
Tennison Road bridge is one of two in South Norwood currently undergoing repairs.
Work to strengthen Penge Road began last summer and is due to finish this month.
Upgrades to the 125-year-old Tennison Road bridge are scheduled to be completed in summer 2015.
The work has already proved controversial, with Network Rail engineers demolishing a children's playground in South Norwood Recreation Ground to make room for building materials and tools.
Representatives of Network Rail and Croydon Council will answer questions at a drop-in session at Speroni's restaurant in Selhurst Park between 5pm and 8pm tomorrow.
Are you concerned about the impact of the closure? Post a comment below or email firstname.lastname@example.org.
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