The move could delay the Aberdeen Western Peripheral Route by up to two years as campaigners fight their corner in the Scottish courts.
Local action group Road Sense are lodging a challenge to the lawfulness of Scottish Ministers’ decision to approve the new road late last year.
William Walton, Chair of Road Sense, said: “The legal opinions that we have received confirm that we have substantial grounds on which to challenge the AWPR through the court process.
“The court process will be the first time that arguments about the means by which the route for the AWPR was identified, selected, appraised and approved will be heard. The court will be the first body to give a detached, dispassionate assessment of the legality of the AWPR as it is proposed.”
Walton called for preparatory work on the proposed route to be halted as soon as the legal challenge is submitted, and said the group would seek an injunction if construction began before the challenge was determined.
The latest legal challenge will frustrate contractors who had hoped the scheme would finally progress after receiving planning permission in December following a local enquiry. Plans for the 28-mile bypass were first put forward in 2003
Cabinet Secretary for Finance and Sustainable Growth John Swinney said: “The AWPR is one of the most important infrastructure projects in the North East, bringing a range of substantial benefits to the region.
“The route will provide a much needed bypass around Aberdeen linking existing major roads and key locations such as the airport, park and ride sites and the major industrial estates around the city. The bypass will reduce congestion in the heart of the city as well as remove thousands of vehicles from the area’s rural roads which are unsuitable for such high volumes of traffic.”
The authorities were planning to approach contractors by the end of this year but that now looks like being delayed by the legal challenge.