Hundreds of people who use the Bristol to Bath cycle track have met to protest over plans to use part of the route as a bus "rapid transport" link.
More people turned-up for the meeting than there was space.
More than 6,000 people have already signed a petition against the proposal.
It was agreed to set-up a campaign group to fight the plans and promote the group's message.
Although it is still only a proposal at present campaigners believe the idea should not be allowed to get off the drawing board.
The venue for the meeting was changed because of the numbers wanting to attend but on Tuesday night organisers had to turn people away from the Easton Community Centre for health and safety reasons.
Under the plans a three-mile stretch between Lawrence Hill and Emerson's Green could be altered to have a "rapid transit" bus lane alongside pedestrians and cyclists.
The West of England Partnership said it needed to get cars off the region's roads but campaigners believe building a bus lane on a cycle route is not the way to do it.
Sustainable transport charity Sustrans said the route, which is used for 2.4 million walking and cycling trips, was the "right idea, wrong route".