A second scheme to dual the A47 in Norfolk could be set for a High Court showdown.
Environmentalists are claiming the Department for Transport's (DfT) decision to permit the £200m dualling of the section between North Tuddenham and Easton was unlawful.
Consent for the dualling of five-and-a-half miles of the road was given last month.
But lawyers for environmental consultant Dr Andrew Boswell have sent a legal letter asking permission for a judicial review.
If a review is granted, the matter would be heard in the High Court.
Judges would then make a decision on whether granting of consent was sound or not.
Dr Boswell, who also launched a legal challenge against the decision to dual the A47 between Blofield and Burlingham, said there were four grounds for the second challenge.
He said: "The first is they have not assessed all of the road schemes planned together for the impact on carbon emissions.
"The second is that it has not been assessed against the carbon budget in Norfolk County Council's Local Transport Plan 4, which has now been adopted."
He said the third was around the colony of barbastelle bats near Ringland and the assumption by then secretary of state Grant Shapps that a bat licence would be granted for dualling work.
A fourth is over whether Mr Shapps was sent the full set of documents compiled during the Planning Inspectorate process.
A spokesman for National Highways said: “Lowering our corporate carbon emissions to net zero by 2030, construction and maintenance emissions to net zero by 2040, followed by all road users to net zero by 2050, are key targets for us as we drive towards a sustainable future.
“We are also committed to no net loss of biodiversity across all our activity by 2025. From that point forward, and including this project, we are focused on increasing biodiversity across the areas we are working.
“These aspects are rightly coming under more scrutiny within the development consent order process to ensure the legacy of our schemes is a positive one; for the environment, the road user and those living and working nearby.
“As such, we stand by our plans and remain committed to investing almost half a billion pounds on a series of improvements to the A47 across the east of England."
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