The Environment Agency has temporarily blocked plans to dismantle a fleet of contaminated former US naval vessels on Teesside.
Four ships have already left the James River in Virginia
Hartlepool-based Able UK has signed a multi million pound deal to decommission 13 ships, creating an initial 200 jobs.
The Environment Agency now says authorisations issued to allow dismantling and recovery of the ships at the Teesside yard are invalid.
But Able UK said it is satisfied it has the relevant permission to carry out the work.
The agency said a new licence would now be needed before the decommissioning could go ahead.
It said a transfrontier shipment (TFS) approval, which is granted by the Agency, had been given on assumption that all relevant permissions would be in place for dry dock dismantling at the yard.
The Environment Agency said it has taken action after it found out several permissions and plans are not in place.
It has advised Able that it should consider its position over the so-called "ghost fleet".
Agency area manager Craig McGreevy, said: "The agency's priority is to make sure that the environment is protected and that all the legal requirements are complied with.
"If, in the future, all the environmental and planning requirements are met, there is no reason why dismantling and recovery of ships should not take place at the Able site."
The Environment Agency said Able UK and the US Maritime Administration are now considering their position.
In a statement, Able UK managing director Peter Stephenson said: "' I can confirm that late yesterday we met with the Environment Agency who indicated to us they had a problem relating to licences issued in connection with our contract with the US Marine Administration."
He said he understood the EA would be writing next week to set out its concerns and was surprised it had contacted the media.
"It therefore makes it very difficult for us to comment in detail on the matter.
"However we remain satisfied that we have relevant planning permissions in place for the recycling of vessels and the creation of dry dock facilities.
"We have applied for approvals from Defra [Department for Environment, Food and Rural Affairs] in relation to work on the dry dock facilities, covering matters such as dredging.
"Given that similar approvals have been given in the past, we are confident they will be in place by mid-November.
"When we do receive the written comments of the agency we will obviously give them careful consideration."
The first four of the ships are due to complete their Atlantic crossing within two weeks.
The deal has seen protests from environmentalists, who claim the fleet is an ecological time bomb.