Liberal Democrats in Kendal have launched a campaign to stop plans to close the footpath which links Rusland Park to Castle Grove.
Network Rail are seeking to infill the underpass which is regularly used by school children to walk and cycle to school safely.
Local county councillor Chris Hogg has written to Network Rail to raise concerns that the plans would see local children having to walk to school via the less safe Parkside Road railway bridge.
Chris said: “The underpass is regularly used by school children, dog walkers and older residents accessing Castle Stores.
“The underpass also contains a much-loved mural depicting the history of Kendal.
“It would be a terrible shame to lose this link.
“Local people must be consulted before any action is taken.”
Local MP Tim Farron said: “These plans are fundamentally flawed and present a huge safety risk for local school children.
“Network Rail really haven’t thought this through.”