A major parcel courier has paused some delivery services into Ireland as well as the rest of Europe - because of pressure caused by new post-Brexit red tape.
DPD became the latest company to warn that the UK's divorce settlement with Brussels had led to more complex processes at the border.
Seafood exporters said they have been hit by a "perfect storm" of bureaucracy, IT problems and confusion following Brexit.
Marks & Spencer said the new rules and regulations are set to "significantly impact" its overseas ventures in Ireland, the Czech Republic and France.
And hauliers described being "overwhelmed" by red tape due to new checks on deliveries to Northern Ireland from the rest of the UK.
DPD said that up to 20% of parcels had incorrect or incomplete data, meaning they had to be returned to customers and announced a pause to its road service into Europe and Ireland until Wednesday.
The company said in a statement:
"In view of this unprecedented set of circumstances, we believe that it is only right to pause and review our road service into Europe, including the Republic of Ireland. During this time, we will work with our customers to validate and correct the data we have in our system, to reduce the delays and enable us to resume normal service.
"This pause in our operation will be as short as possible and we intend to recommence this service on Wednesday, January 13."
M&S boss Steve Rowe warned that the trade agreement between the UK and the EU is causing problems with "potential tariffs on part of our range exported to the EU, together with very complex administrative processes".
Haulier industry body Logistics UK said deliveries were being delayed as lorries arrived in Belfast with incomplete paperwork.
In order to avoid a hard border with the Republic, Mr Johnson agreed Northern Ireland would remain in the EU single market - but that has meant checks on goods arriving from Great Britain.
The UK’s Labour Party accused the Government of failing to properly prepare for the end of the transition period on December 31.
A UK Government spokesman said: "Businesses and hauliers have made huge strides to get ready but we were always clear that there would be some disruption at the end of the transition period.
"Although many businesses have moved goods successfully since January 1, we are aware of some issues and are providing guidance and support.
"Hauliers can use our 'Check an HGV is ready' service to make sure they have the correct paperwork and must obtain a Kent Access Permit if they plan to travel via Dover or Eurotunnel."