Welsh transport chiefs have told Pembrokeshire's Assembly Members that the county must prove the A40 needs dualling.
Angela Burns and Paul Davies met deputy first minister Ieuan Wyn Jones and the head of transport for the Welsh Assembly Government to discuss the issue.
"We were told that we should talk to Pembrokeshire Council and businesses and to come back with a business plan for dualling the road," said Mrs Burns.. " The comment was also made that the Irish should probably contribute as they would benefit the most."
The AMs were told that the A40 was not considered busy enough for dualling, even though the traffic levels already exceeding Department for Transport maximums for a single lane carriageway.
Mr Davies added: "I told them that there is already more traffic using the road than the upper limit set by Government but they will not have it. They have so far refused to consider dualling the road.
"It makes economic sense to upgrade this crucial artery and it would also make the road safer."
The Conservative AMs were surprised by the request to prove the need for dualling.
"The statistics clearly show that this road is busy enough to justify dualling, to tell local businesses and the council to come up with a business plan is a cynical ploy to get us to be quiet – the economic need for dualling has already been proven beyond doubt," said Mr Davies.