Tánaiste and Minister for Enterprise, Trade and Employment Leo Varadkar is writing to every business in Ireland urging them to prepare for the change in relationship between Britain and the EU.
The letter has been sent to the roughly 225,000 businesses registered with the Companies Registration Office.
In it, Leo Varadkar advises companies to get to grips with the impact Brexit will have on their supply chains, cash-flow and customs requirements.
The letter also explains how firms can get an Economic Operators Registration and Identification number, which is required when importing or exporting goods into and out of the EU and other longer-term financial management issues.
The letter also includes all relevant information and contact details to help businesses access Government grants and advice that are available.
The Tánaiste said the UK left the European Union on January 1 this year. But because of the Withdrawal Agreement and the transition period, most businesses, workers and citizens did not experience any immediate changes, but he cautioned that is about to change in a very big way.
"Great Britain will leave the EU single market and customs union on the 1st of January next year. That's now fewer than three months away," Leo Varadkar said.
"I’m writing to all businesses and asking them to make sure their business is ready for the significant change this will bring for them, their staff and their customers," he stated.
"2020 has been a year like no other. I know that Brexit is yet another challenge for businesses, after what has been an exceptionally difficult few months. However, we must prepare now," the Tánaiste urged.
"The Government is here to help with money, training and advice available. This letter today is about helping as many businesses as possible to access these significant measures," he added.