Shipbuilding Union GMB has accused MP Geoffrey Cox of "dereliction of duty" for allowing the Appledore shipyard to close on his watch.
The North Devon facility is due to shut on Friday (March 15th) with the loss of 200 jobs.
The closure is despite strenuous efforts by Unions and campaign group Friends of Isles of Scilly Transport to secure an order for a Scillonian ferry to be built at the yard.
GMB has now said that West Devon MP Geoffrey Cox, who is also the Attorney General, "seems to be so busy tying himself in knots over Theresa May’s bad Brexit" that he has forgotten his own constituents.
The Union said in a statement yesterday: "On Friday Appledore will fall silent - losing jobs, skills and a way of life. GMB has campaigned to stop the closure since it was announced last year, handing in a 10,000 strong petition to Parliament and suggesting several plans to keep the shipyard viable.
"Local MP Geoffrey Cox met with GMB in October, but despite his warm words he seems happy to let the famous yard, and 200 jobs, leave his constituency."
Mike Payne, GMB Regional Political Officer Wales and South West, said: "Appledore has been part of the fabric of North Devon for hundreds of years - but the attorney general seems content to let it die.
“We have written to Mr Cox demanding action - his failure to protect this proud shipyard is a dereliction of duty.”
Friends of Isles of Scilly Transport, aka FRIST, recently said that it was 'seriously disappointed' that efforts to save the shipyard with an order for a new Scillonian ferry had not succeeded.