The Wandsworth Common station footbridge could be closed to the public by the end of the week, as work to move ticket barriers began on Monday morning.
The footbridge has been open for public use for decades, according to campaigners, but the railway company intends to close it off to stop fare dodgers.
December 22: Wandsworth Common footbridge could be blocked off in attempt to stop fare dodgers
Sarah McDermott, a Conservative councillor for Nightingale, and one of a group that has launched a petition to save the footbridge, said the bridge was a "well-used route for numerous years".
She said: "Nightingale councillors were dismayed to hear that Southern is planning to stop residents going about their daily lives crossing the footbridge from Wandsworth Common to Jaggard Way.
"This has been a well-used route for more than 20 years and probably ever since the station was built.
"Nobody from Southern Rail has contacted us directly as the local councillors.
"Residents and businesses are signing our petition in significant numbers.
"I am sure it is perfectly feasible to have ticket barriers to prevent fare dodgers and a through route for local people."
David Dean, Conservative candidate for Merton and Wandsworth in the London Assembly said: "Southern Rail's engagement team has contacted me directly with regard to their shoddy service.
"When we meet, I will be adding my voice to many others stating that their franchise contract is based on providing a good service.
"Treating residents with respect is clearly one of the key aspects of it.
"In addition, I will be making clear residents' anger at this proposal. I expect them to listen and modify their plan."
A Southern spokesman said: "We have discussed alternative proposals with the council but unfortunately, none of these are workable due to layout constraints of the station.
"We continue to liaise with the council on this project."
The Wandsworth Guardian is awaiting details on how many people have signed the petition.
To view the petition, go to https://www.surveymonkey.co.uk/r/wcfootbridge
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