Brexit rules could mean extra checks on the movement of military hardware between Great Britain and Northern Ireland, unionists have warned.
The Ulster Unionist Party (UUP) says new Irish Sea shipping arrangements require the Armed Forces to give 15 days' notice, complete customs declarations, and even inform NATO before moving the equipment.
UUP MLA Doug Beattie, who is also a former soldier, said that the "ludicrous" restrictions were a consequence of the Northern Ireland Protocol, which has governed the movement of goods across the Irish Sea since the Brexit transition period ended.
Under the terms of the protocol, Northern Ireland remains in the single market for goods and continues to apply EU customs rules at its ports and airports.
Mr Beattie said: "As of 1 January, any movement of materials and equipment from Great Britain will be required to give 15 days' notice and complete a customs declarations form.
"Even more incredibly, to move from Great Britain to Northern Ireland they will have to complete a NATO form that is designed for movement of NATO forces around the globe.
"This shows how ludicrous and unacceptable the outworking of the Northern Ireland Protocol are in practice.
"This should not merely be a Northern Ireland issue but it should be of serious concern for every MP at Westminster, no matter what party they represent."
On Friday, Democratic Unionist First Minister Arlene Foster contacted Defence Secretary Ben Wallace to express concern.
Mrs Foster said a restriction on the movement of military equipment was among "hundreds of problems" created by the protocol.
"It's not acceptable that military movements within the United Kingdom should be affected in the way that has been reported," she said.
"It's just an example of the hundreds of issues that have been raised and we'll continue to work through those issues and be focused on each of them.
"However, there needs to be a replacement to this protocol and we need to find a way forward that is sustainable, because what we have at the moment is unworkable."
Addressing the media in Co Fermanagh, Mrs Foster said the idea of NATO having a say on the movement of military equipment within the UK was "completely outrageous".
A spokesperson for the Ministry of Defence (MOD) said: "The Northern Ireland Protocol does not place limitations or restrictions on the Ministry of Defence's ability to do their duties. These are essential state functions, which the Protocol respects."