Friends of the Earth Cymru have confirmed today that a letter will be sent to the Welsh Government, asking them to withdraw and restart an environmental consultation about the proposed M4 relief road route.
The group say they are concerned about the environmental impact of the proposals, and claim alternative routes to the one through the Gwent Levels - which was announced as the preferred road earlier this month - were not given enough consideration.
The Welsh Government has two weeks to respond to the letter, and depending on the outcome of that, Friends of the Earth may decide to then begin judicial review proceedings.
Ministers have previously said they expected to face a legal challenge.
More top news
A cold night with a yellow warning in force for snow and ice. Winds will remain strong but a largely dry and bright day tomorrow.
In the first of our specials looking at the Welsh education system, we visited a new primary school in Llanelli.
A six-part series following the lives of the people who live and work in the shadow of Snowdon, one of the busiest mountains in the world.