Pembrokeshire County Council has made history by triggering the Welsh Assembly Government's first ever special assembly procedure committee.
The committee is meeting to decide whether the Robeston Wathen by-pass should be a dual carriageway or a three-lane road. And the council's view that the road should be dualled has been backed by Preseli Pembrokeshire AM Paul Davies.
"I fully support the council's decision to object to this order and wish them every success," said Mr Davies.
"The council is quite right to argue that it is unsustainable to build a road which in all likelihood will need updating in a few years time."
The County Council's objection to a Government order for the three-lane road has led to the first special Assembly
procedure committee in the Assembly's 10 year history. The committee, made up of five cross-party AMs, finishes hearing evidence this week and is expected to announce a decision sometime in November.
"The Conservatives have long argued that the A40 needs to be dualled for economic and safety reasons," added Mr Davies.
"The council, ourselves and the local residents all want a dual carriageway which will set the design standard for any future improvements to the road."