Concern over £1bn M4 relief road options
Concerns have been raised over plans for a £1bn M4 relief road to ease traffic congestion around Newport.
All three routes involve a new road to the south but not enough attention has been paid to an alternative solution, said the assembly's environment committee chairman.
Alun Ffred Jones's letter to the transport minister also raises environmental and financial issues.
The Welsh government said the minister would respond in due course.
Last year, a transport expert suggested improving the existing roads could bring similar benefits, at a lower cost.
Traffic jams on the M4 around Newport are a regular problem for businesses and commuters.
The Welsh government's proposed long-term solution is a relief road.
But it would be expensive and environmental groups are worried about its potential impact.
Plaid Cymru AM Mr Jones, chair of the Environment Committee at the Welsh Assembly, told BBC Radio Wales: "There are a great many concerns across the board, across parties, about the way this consultation has been taken forward.
"That is why we're seeking clarification, and then from that, the committee can make up its own views."
IS THE 'BLUE ROUTE' AN ALTERNATIVE?
• This would involve an upgrade of the A48 Newport Southern Distributor Road (SDR) and the former steelworks road
• Roads would be re-constructed as a two-lane, dual carriageway at motorway or expressway standard
• It would be widened to a three-lane motorway in future if needed
• The route would follow a line between the Magor Junction 23A to the east of Newport to Tredegar Park Junction 28 to the west of the city
Source: Institute of Welsh Affairs
Mr Jones said people giving evidence to his committee claimed the Welsh government may have broken European rules by not putting sufficiently distinctive options in its consultation.
He is asking whether the so-called Blue Route, which involves upgrading existing roads, is being seen as a "reasonable alternative".
The committee is planning to publish its report about the environmental impact of the proposed new road before the summer break.
Mr Jones said a number of concerns had been raised about the assessment of potential environmental impact in the plans.
A spokeswoman for Transport Minister Edwina Hart said she would respond to the letter "directly, in due course". Mr Jones said he wanted a response by Friday.
The Federation of Small Businesses said it had given evidence to the committee and "we will be keen to see the economy, science and transport minister's response to this letter, and the many questions that it raises, by the committee's Friday deadline".
Chancellor George Osborne has called the relief road one of the most important road schemes in the UK.
Plans to ease congestion at the bottleneck gateway to south Wales were first unveiled in 2004.