A group has been set up by people in South Queensferry, led by leading engineer John Carson who has drawn up plans for an innovative "tube tunnel" across the estuary's seabed.
The Forth Tunnel Action Group (Forth TAG) plans to lobby MSPs and the Scottish Executive's national transport agency, Transport Scotland, as well as organising local meetings and mail shots to get its message across. Members hope to make the debate a key issue of next year's parliamentary elections.
Mr Carson has been joined by businesses, community representatives and the local councillor in pushing for the option to be chosen in place of a new bridge.
The South Queensferry resident and former head of Miller Civil Engineering revealed his plans for a tube tunnel earlier this year.
He said a tunnel built in a dry dock, such as Rosyth, then floated and sunk into place on to the bed of the estuary would cost less than a bridge, would be more environmentally friendly, and would take just three years to build.
Experts have told him the structure would cost around 400 million, plus up to 80m for approach roads. A traditional bored tunnel could be up to 100m cheaper, however consultants have previously said this would run in to geological difficulties.
A new bridge, with dedicated lanes for public transport, is currently priced at 360m at 2004 prices, but this rises to 600m with the related infrastructure.
Due to the number of houses surrounding the existing bridge, and geological problems, a tunnel would need to be built further west than South Queensferry, possibly between Pattiesmuir in Fife and the M9 at Old Philpstoun.
This appeals to residents keen to protect South Queensferry from further disruption, while city politicians are also concerned about thousands of new commuters clogging up roads.
Mr Carson said: "My original decision to talk to a local community council meeting was born out of the frustration I felt every time I picked up a newspaper and saw the third Forth crossing described as a bridge.
"Our consultants advise us that a bridge would be the most environmentally damaging - in part because the mud flats adjacent to a new crossing are of international interest and are protected by EU regulations."
No decision has yet been made on a new crossing, but the existing Forth Road Bridge could be forced to close by 2019 because of corrosion in the main cables.
Ministers have ordered studies into a new crossing to be speeded up so they can take final decisions on the project in less than a year's time, and Transport Scotland has agreed to investigate the tunnel option as part of this.
Forth TAG currently consists of Mr Carson, deputy chairman of the Queensferry Community Council Keith Giblett, a local traders' representative and Lib Dem councillor George Grubb.
"I feel another bridge would be a great intrusion into South Queensferry," said Councillor Grubb.
But the Forth Estuary Transport Authority, which runs the existing crossing, favours a new bridge.
FETA general manager Alastair Andrew said: "Research conducted for Feta tells us that the most efficient, cost-effective and environmentally friendly way of delivering such a multi-modal crossing would be a second suspension bridge at Queensferry."