Supporters who have lobbied for the scheme for 16 years have called for the work to be accelerated to encourage drivers to switch to cycling and walking.
They are now asking local MSPs to press East Lothian Council to move faster.
The proposed four-mile scheme would bypass the busy B1345 road between the seaside village of Gullane and Drem station on the North Berwick-Edinburgh line in East Lothian.
The campaign is backed by local businesses such as restaurateurs Tom and Michaela Kitchin, who own The Bonnie Badger hotel in Gullane.
In a letter to East Lothian SNP MSP Paul McLennan and south of Scotland MSPs Craig Hoy (Conservative) and Martin Whitfield (Labour), the campaigners wrote: “Our campaign commands overwhelming public support among residents and the business community.
"It is essential that local families and visitors to the area are given a healthy alternative that will allow safe travel between the villages of Drem and Gullane as part of a comprehensive network of such routes across the county.
"Note also that Gullane is becoming the size of a small town thanks to the hundreds of houses being erected near the proposed path.”
However, campaign spokesman Iain Monk said it had been told by the council that construction “would not start for ‘years’, at best in 2024” because of the grant application processes and the technical assessments required.
He said: “This timescale has shocked us and we believe contradicts the council’s publicly-stated position of improving active travel infrastructure urgently in light of the recognised climate emergency.
“All the more so as our country will be hosting the Cop26 summit in November, and yet here, within 70 miles of the conference centre, we have an example of how global statements, agreements and policies as to the importance and urgency of creating active travel infrastructure to reduce greenhouse gas emissions seemingly do not flow down to actual results at the local level.
"It's an extremely dispiriting story.
“It is vital that construction starts as soon as possible.
"Council leaders must show political leadership and compress this unacceptable timescale.”
An East Lothian Council spokesperson said: “We are pleased to be continuing our work to identify and deliver active travel options across East Lothian, building on projects from recent years.
“We are awaiting confirmation from [path developers] Sustrans of the process to fund feasibility work with a view to taking a fresh look at the potential options for developing a safer link to cycle between Drem and Gullane.
"We look forward to providing an update on this in due course.
“Our climate change strategy sets out the council’s commitment to tackling the climate emergency with specific outcomes, key priority areas and actions over an initial five-year period towards achieving these overall aims.
"We have continued to reduce our carbon footprint and deliver actions identified within the action plan which contribute towards us becoming a net zero council.
"Key achievements in the last year include the launch of the East Lothian Energy affordable energy tariff, progression of the installation of solar PV [photovoltaic cells], an increase in the local recycling rate, our electric vehicle fleet and public charge points.”