Traffic measures have been introduced on a major road leading to Holyhead port as the UK prepares to enter its new trading relationship with the EU.
The Welsh Government has said the plans are aimed at “minimising any possible disruption to the port, town and wider community”.
Freight turned away from the port due to incorrect documentation will be sent on to the westbound A55.
The UK Government predicted this could be up to 70% of freight.
Holyhead is the second busiest roll-on/roll-off port in the UK, behind only Dover.
The Kent port has seen gridlock over recent weeks as Britain approached the end of its transition period with the EU and France banned all Channel crossings over the new coronavirus variant in the south-east of England.
A trade deal between the EU and UK has now been agreed and will take effect from 1 January, but the changes in the trading relationship between the two parties mean there could be some disruption.
Chair of the CBI in North Wales Kinza Sutton told BBC Radio Wales: “We anticipate that there will be delays.
“Certainly the changes to documentation is going to cause huge changes for everybody, so certainly during January I’d imagine there will be delays as everyone gets used to the new systems.”
Daniel Lambert, from wine importer Daniel Lambert Wines, based in Bridgend, added: “There’s going to be a lot of friction.
“I think the lorry fiasco just before Christmas had a massive impact on… stock that we were expecting for January – some of our promotional stock for January is still not here.”
The Welsh Government added it expected the peak of traffic issues to be in mid-January.
Any HGV traffic turned away from the port will be directed to the A55 at junction four. Lorries will be stacked if there is no other site available.
A plan to buy a truck stop as part of post-Brexit customs checks was scrapped on Christmas Eve.
The eastbound carriageway between junction two and four will run with contraflow.
Economy Minister Ken Skates said: “We need to implement these contingency plans in order to do what we can to minimise any possible disruption for the port, community of Holyhead and wider area.
“We have never faced this kind of situation before and we have a duty to prepare for the worst possible scenario.”