Customs authorities in the Republic of Ireland have announced a temporary relaxation of rules to help keep trade flowing from Great Britain.
Traders shipping from to Ireland must complete a range of new post-Brexit paperwork.
It is causing problems, with trucks not being allowed to board ferries or facing delays arriving at Dublin Port.
Hauliers will be able to use an override code to complete a piece of administration known as ENS.
Andrew Kinsella, managing director of Gwynedd Shipping in Wales, told the BBC on Thursday that his company has a backlog of 60 lorries waiting to be shipped to Dublin.
He said many hauliers were finding that their customers are not able to generate the declarations that are needed to ultimately enable a lorry to get onto a ferry.
“Whilst you don’t see queues at ports and terminals, the reality is that these queues are developing elsewhere – in our depot in Holyhead; in our depot in Deeside and in our depot in Newport in south Wales and lots of hauliers have depots in the proximity of ports,” he said.
“There are a lot of issues about demarcation about who is going to arrange the export declaration with the UK revenue authorities, who’s going to arrange the import declaration, the hauliers then trying to arrange the import safety and security declaration to create an ENS number which helps you generate a PBN [pre-boarding notification] number.
“So there has been a lot of everyone finding their feet”.
The letters ENS refer to an entry summary declaration, an online form which goods carriers are now legally obliged to submit to Irish customs when transporting goods from Great Britain into Ireland.
On Thursday night the Irish Revenue Commissioners said it recognises that “some businesses are experiencing difficulties on lodging their safety and security ENS declarations”.
It said that in response it was providing a “temporary easement” which would allow an ENS to be produced without all the normally required information.
Meanwhile Stena, the ferry company, said it was cancelling a dozen sailings between Wales and Ireland next week due to “a decline in freight volumes during the first week of Brexit”.
By John Campbell
BBC News NI Economics & Business Editor