Network Rail has submitted plans to erect a safety fence to protect employees carrying out work on the Knaresborough Viaduct.
But people in the town claim the alterations to the Grade II listed structure could majorly obstruct the view.
John Richards, chairman of Knaresborough Civic Society, said: “This is one of Yorkshire’s most iconic views and this change will alter it for the worse. It could potentially harm Knaresborough’s tourist appeal.
“The proposed development will add steel posts to the viaduct and a wire fence. These materials and the plans shown are not in keeping with the character of the structure and would cause a significant visual detriment.
“The civic society wants to ensure workers on the viaduct are safe, but notes that the report included with the application does not say that any specific risk has been identified in Knaresborough.”
Resident Diane Maguire, added: “The viaduct is an iconic view and it’s something that I think visitors come to Knaresborough for. They know about the view because it’s on postcards and calendars.
“If it is to protect workers why does it need to be permanent because they won’t always be up on the bridge? Also why aren’t they already protecting their workers under health and safety regulations.”
The plans would see steel posts and a single wire built between the parapets of the viaduct. Currently the maximum height of the parapets are 88cm, which falls 37cm short of Network Rail’s standard specification.
A Network Rail spokesperson said: “As part of our ongoing bid to improve the safety and working conditions for our employees we have identified that the height of the parapets at the viaduct need raising slightly to give a better level of protection.
“We recognise the significance and history of the viaduct and intend to keep the visual impact of any additions to it to a minimum.”
The spokesperson pointed out that a similar safety fence had recently been installed on the listed Royal Border Bridge in Berwick.
However Mr Richards said: “Given the rare instances work takes place on the viaduct, we feel temporary fencing could be put in place on these occasions that would have no permanent adverse effect.”