Campaigners calling for naval supply ships to be built in Britain today blasted “secrecy” surrounding the deal.
The Government is preparing to place a £1.6billion contract for three Fleet Solid Support vessels which will restock Royal Navy warships at sea.
But unions fear much of the work will go overseas - depriving UK staff of hundreds of millions of pounds’ worth of contracts.
They accused the Ministry of Defence of “gagging” companies bidding for the bumper deal - intensifying fears of foreign involvement.
Confederation of Shipbuilding and Engineering Unions general secretary Ian Waddell said questions he sent to the four consortia hoping to win the race have gone unanswered.
“We wrote to each of the bidders with five key tests showing the social value of their proposals and we were told more than once that the MoD had asked them not to respond to the request, in addition to any commercial non-disclosure agreement that might normally be signed,” he said.
“What is the MoD trying to hide?
“Workers are starting to draw the conclusion that this contract is shrouded in secrecy because the Government has already made a political choice that will mean jobs will go overseas and promises about UK workshare will never materialise.
“We have been concerned for some time that the MoD is preventing an open, honest and transparent procurement of these ships.”
The 40,000-tonne Royal Fleet Auxiliary vessels will resupply Royal Navy warships, including the £6.2bn Queen Elizabeth-class aircraft carriers, with food, ammunition and explosives.
Four consortia were each given £5million by the Ministry of Defence to develop their bids as the Government began the “competitive procurement phase”.
The shortlist includes Team UK, involving Babcock and BAE Systems; Mumbai-based Larsen & Toubro, which describes itself as “India's premier infrastructure developer”; Dutch firm Damen Group; and Team Resolute, led by Spanish shipbuilders Navantia.
Team UK estimates 2,000 British jobs will be safeguarded if it is awarded the contract, with 1,500 more protected in the wider supply chain - and another 2,500 jobs indirectly benefiting in communities surrounding the yards.
Military expert Francis Tusa believed Spanish firm Navantia could land the jackpot deal, with parts made abroad assembled in the UK.
Mr Tusa, the editor of Defence Analysis, said British workers may only benefit from a “limited build” or “integration” process which would be “to put it mildly, tin-eared”.
He added: "It simply seems astounding that at a time of economic uncertainty that the Royal Navy should be so keen to shovel hundreds of millions of pounds to Spanish shipyards, and is risky.
"The FSS ships are warships, and the policy is that warships will be built in UK yards. It's a pretty straightforward policy - so implement it.”
Labour has said it would give the contract to British shipyards.
An MoD spokeswoman said: “It is categorically untrue to suggest that non-disclosure agreements (NDAs) were placed on bidders in the Fleet Solid Support competition to try to make sure that issues such as UK workshare and intellectual property do not get raised in public.
“NDAs are normal in commercial competitions to protect disclosure of sensitive information.
“The Fleet Solid Support contract will be awarded to a UK business, either solely or as part of a consortium, promoting growth and stimulating investment across the UK shipbuilding sector.
“A significant proportion of the build work will be carried out in the UK including integration.
“This contract will maximise the social value contribution shipbuilding can make in the UK, whilst balancing value for money.”
