Bank of Ireland said it was urging companies to consider their cashflow, currency and customs.
The bank said new arrangements were likely to bring increased costs. For example, changes to business processes related to customs compliance and changes in the supply chain could result in increased working capital requirements, it said.
And an increase in exchange rate volatility is another potentially significant impact, the bank added. Customs issues to be taken care of included availing of trader support services, supplier management, trade tariff codes and getting an Economic Operators Registration and Identification (EORI) number.
The bank s Niall Devlin said: We truly hope for a deal, but whatever the outcome, how NI businesses operate will change from January 1.