Up to 90,000 businesses that are expected to be impacted by Brexit will be contacted as part of an intensified programme of engagement by Revenue over the next week.
Revenue said its focus is on helping and supporting businesses that will be immediately impacted by Brexit from January 2021.
The letters set out the critical Brexit preparation steps businesses need to take now.
These include being registered for customs by getting an EORI (Economic Operators Registration and Identification) number, as well as cashflow and financial analysis to be ready for customs tariffs.
Lynda Slattery, Head of Revenue's Brexit Policy Unit, said Revenue are engaging with businesses that will be impacted by Brexit, whether they are involved in imports or exports to or from the UK or transiting the UK for imports or exports that originate from or are destined for the European Union.
She said that Revenue's message is simple.
"Brexit will be a reality from 1 January, there will be no change in that date, your business needs to be ready and you need to get ready now," Ms Slattery stated.
She said that Revenue is providing what it hopes is a helpful checklist for businesses that they should work through carefully and fully.
"A key starting point, still to be completed by some businesses, is registering for customs. The EORI registration process can be completed quickly through the Revenue Online Service (ROS) and a guidance video is available on www.revenue.ie/brexit to bring you through the process," she explained.
"We will be following up on the letters being sent to businesses in the next week with a targeted telephone contact with businesses that are the most exposed business in terms of Brexit readiness," she added.
Revenue also said that in collaboration with the Department of Agriculture, Food & the Marine and the Department of Business, Enterprise & Innovation, it will host a number of Brexit information webinar sessions to support businesses in identifying and understanding the implications of Brexit and what they need to focus on in getting Brexit ready.
These are scheduled for October 5 and 6.
Registration information for the webinars is included in the letters being sent to business and is available on Revenue's Brexit webpage www.revenue.ie/brexit."