A long-running campaign to open an abandoned railway tunnel has been stepped up after plans to close up its entrances were lodged.
Queensbury Tunnel runs 1.4 miles (2.3km) between Bradford and Halifax in West Yorkshire and has been partially flooded and collapsed.
Highways England said it had submitted the application "for further safety work" to close the tunnel.
Campaigners want to reopen it as part of a cycle network.
A planning application for "securing and infilling of the shafts and entrances of Queensbury Tunnel" has been made to Bradford Council.
Norah McWilliam, of Queensbury Tunnel Society, said it was "a remarkable public asset".
"We will have failed future generations if the opportunities presented by the tunnel are allowed to slip through our fingers", she added.
The society has asked for objections to be made via the council's planning website, it said.
It is also campaigning in the village of Queensbury, which sits above the tunnel.
Bradford Council said the application would be processed under normal planning laws and policies.
"Independent of that process, as approved by the council's executive committee, we believe the tunnel can still form part of a Bradford to Halifax greenway", the council said.
It had requested a meeting with Highways England, and would make the case for a pause in sealing the tunnel for potential funding to be explored, it added.
Highways England said: "The safety of the community and our contractors is paramount and the Department for Transport, the owners of the tunnel, agree that this work to close the tunnel should be undertaken as soon as possible."
The first phase of work to strengthen the most vulnerable areas of the tunnel was almost complete, it added.
- Opened in 1878, the tunnel was last used by trains more than 60 years ago
- It took four years to build with the loss of 10 lives
- On completion, it was the longest tunnel on the Great Northern Railway