Irish customs authorities deny they are holding up goods supplies entering the Republic from Great Britain, blaming companies for failing to fill in the paperwork.
Irish Revenue says that 76% of goods were getting cleared within 30 minutes of ships arriving to Dublin Port yesterday morning, and that freight traffic is at record lows for this time of year.
"We have processed thousands of declarations," said Tom Talbot, head of operations for customs at Dublin Port. "On Sunday, we had 40 trucks parked up in a port that has a normal traffic of 1.1m freight vehicles through it."
But one industry source said drivers are being held up for hours or even days at a time in Dublin over customs formalities, a situation that is being compounded by Covid restrictions.
And Logistics UK, which represents UK drivers, retailers and manufacturers, says consignments of different goods that are "grouped" together in the same container are facing particular problems crossing the Irish Sea.
The head of the Irish Road Haulage Association, Eugene Drennan, said most of the delays are down to "cumbersome" IT systems and new rules that were not "tried and tested" in time.
"The biggest flaw in it all is that the Irish system does not talk to the English system," Mr Drennan said. "There might be no problem now because there are no goods. But it's on the way."
One driver turned up for health and safety clearance on Saturday with no paperwork, and had to wait 36 hours until a customs agent was available to provide it.