£1bn M4 relief road 'risks Newport docks jobs and trade'
A £1bn new M4 relief road through Newport's dockside could put jobs and future investment at the site at risk, says Associated British Ports (ABP).
Transport Minister Edwina Hart has defended her decision to invest in a new motorway south of Newport.
ABP's Matthew Kennerley said his firm would lose land and one dock would have up to 60% of vessels unable to use it.
A Welsh government spokesman said: "We are committed to this ambitious infrastructure project."
Ms Hart has said she expects to face a legal challenge after announcing the go-ahead for the new road, to run between Junctions 23 and 29 of the M4 and to include a new bridge to the south of Newport.
To be completed by the spring of 2022, the project would be the largest capital investment programme ever announced by the Welsh government.
Seen by some as the answer to crippling traffic congestion into south Wales, it has won the backing of the business group, CBI Wales.
Chancellor George Osborne has called the relief road one of the most important road schemes in the UK and UK ministers have since agreed Welsh ministers can borrow money needed to fund the scheme.
Environmental and some business groups have criticised the proposed route as unnecessarily damaging and costly.
Mr Kennerley, port director of ABP in south Wales, told the BBC programme Wales at Work the proposed road would have an impact on jobs and could make the company less likely to invest in the site in future.
He said: "We don't think it's a great idea to put the new route through the centre of Wales' most important general cargo port.
"We believe there is an alternative route and we presented that throughout the consultation process as a route slightly further north.
"That would still have an impact on the port but to a much lesser extent because it would not be bisecting very important quayside areas.
"As it stands at the moment, the impact on the port would be very serious indeed."
Mr Kennerley said that as he understands the plans, up to 1,000m (3,000 ft) of quayside north of the proposed new motorway bridge would have height restrictions on up to 60% of vessels currently using it.
The Welsh assembly's cross-party environment committee says it has "grave concerns" about Ms Harts's announcement, while Plaid Cymru has withdrawn from budget talks with Welsh ministers in protest.
Opponents have criticised the plan because of its environmental impact and one group has dubbed it a "billion pound mistake."
Three routes were under consideration before Ms Hart made her decision. The other two were further north.
A fourth, the so-called blue route, an upgrade of the A48 Newport Southern Distributor Road (SDR) and the former steelworks road, was proposed during the consultation but was dismissed as one that could not "reasonably deliver the objectives" of easing congestion.
The Welsh government added: "The M4 project is of vital importance to the economic prosperity of the country as a whole.
"In the past, we were unable to progress the scheme because it was simply unaffordable - but thanks to the new borrowing powers we have secured, we can now take forward this and other vital schemes."