They call on National Highways to take public safety seriously and want an urgent review of the Regional Cycle Route 90 from Brighton to Lewes.
This runs on the north side of the A27 and forms part of an almost continuous near traffic-free route from Brighton seafront to Polegate and thence to Hailsham and Heathfield on the Cuckoo Trail.
Sheila O'Sullivan from Cycle Lewes points out the route is hard up against the 70mph carriageway with no protection for people using it.
She goes on: "In stark contrast, work overseen by National Highways to alter the slip roads to the eastbound petrol station, where the new Greggs is to be built, has seen one lane of the A27 closed, a 40mph limit imposed and huge barriers erected to protect workers."
A campaign 'Fix the Route' has been launched to highlight the issue and Lewes MP James MacCleary is backing it.
He says: "I've long been concerned about the safety of this vital route along the A27 and the impact it has on local residents. National Highways must now take an urgent look at this stretch and produce a workable plan. With Parliament sitting again I will be raising this with the minister to push for real progress."
Sheila O'Sullivan goes on: "This path forms a key link in a route that will soon stretch from Brighton seafront to Polegate and beyond, yet it is unsafe and unpleasant to use with people buffeted by 70mph traffic just inches away, blinded by headlights and subject to a deafening road.
"While crash barriers are provided for cars and lorries, none are provided for the protection of people cycling and walking along here.
"The danger the road poses to path users can be seen by the precautions taken by National Highways to protect workers. Yet they do not exercise the same duty of care to people using the path. This needs to change and urgently."
"Get this right and we could see the route rocket, as the success of the new path south of the A27 between Firle and Polegate shows. Given how it serves two universities, the Amex stadium, the South Downs Way and Stanmer Park it should be much busier than it is.
"Improving this route would be good for the local economy, for our health and increase opportunities for people[oe to enjoy the South Downs and provide a cheap and quick way to get between Brighton and Lewes."
Issues include the route being too narrow, too close to the road (failing to meet the minimum required separation from the road for much of its length;) no physical protection for path users; crossing two slip roads (the petrol station and Greggs;) poor maintenance and signs in the path which narrow it."
The organisations involved in the campaign include Transport Action Network, Cycle Lewes, Bricycles, Brighton and Hove Cycling UK, the Cycling Advocacy Network and So Sussex.
National Highways have been approached for comment.