Almost 70% of some agri-food businesses involved in the export of goods to the UK have not yet registered with Revenue to allow them to continue to trade after January 1st.
The Minister for Agriculture has urged businesses to register for an EORI number, saying there was need for "urgent action" from businesses.
Of the almost 4,600 businesses in the agriculture, forestry and fishing sectors, just 1392 have registered for an EORI number.
An Economic Operators Registration and Identification system number will be needed to trade with Great Britain after it leaves the EU on January 1st next.
72% of food, beverage and tobacco manufacturers have registered for an EORI, according to a report from Revenue, which has been seen by RTÉ News.
Regardless, of the outcome of negotiations between the EU and UK new customs formalities and regulatory requirements will kick in from January.
The Revenue figures also reveal a surprising statistic with regard to businesses involved in the repair of cars and motorcycles.
Just 35% of wholesale and retailers involved in the sector have registered for an EORI.
Many of those businesses depend on imports from the UK to carry out their work.
Speaking in Dublin this afternoon the Minister for Agriculture Charlie McConalogue urged businesses to make contact with his Department immediately to begin the registration process and seek advice on trading post Brexit.
Revenue has said that it has identified around 9000 businesses here that traded goods with the UK both last year and this year.
It says the only conditions under which businesses could avoid have to register for an EOIR are; businesses that trade only with Northern Ireland - no customs formalities will apply to such trade, businesses that move goods directly to mainland Europe rather than transiting the UK, or businesses that switch from sourcing supplies in the UK to sourcing supplies in the EU with subsequent direct transport of those supplies to Ireland rather than via the UK.
32,000 businesses have registered with Revenue since January last year.
Revenue says that 97% of the value of export trade to the UK and 94% of the value of the import trade from the UK is undertaken by businesses with an existing customs registration.
It is also warning people to prepare.
It warns that businesses who have not prepared for Brexit or who have not yet fully completed or thought through their preparations will be immediately impacted on 1 January 2021.
Companies may not be able to access key supplies or stock or will not be able to export their goods to and continue to trade with the UK, excluding Northern Ireland.
Companies moving goods to other EU countries using the UK landbridge will also be impacted and will not be able to move their goods if they do not register for an EORI.