The next 11 months will be critical to the state of the Northern Ireland economy "for the next generation" as the UK and EU negotiate their future trading relationship, it's been claimed.
Stephen Kelly, the chief executive of Manufacturing NI, spoke after a speech by Michel Barnier at Queen's University, Belfast in which the former EU Brexit negotiator said that Brexit would bring "consequences" for the UK.
Mr Barnier, delivering the William J Clinton Leadership Lecture in Belfast, said he believed the protocol contained in the withdrawal agreement was good for Northern Ireland, but added: "Brexit will always be a matter of damage limitation and no single person has ever convinced me of the added value of Brexit."
But Mr Barnier said he would continue to listen to the voice of business as the UK and EU embark on negotiating a free trade agreement after the UK leaves the EU on Friday.
However, he said there would be checks and controls for goods entering NI from Great Britain.
Mr Kelly said business was "not done" putting its case on securing unfettered access to the UK market. "What happens in the next 11 months is critical to what happens to our economy for the next generation," he said.
And he added the "consequences" referred to by Mr Barnier meant "the way in which we do business in NI is going to change".
Mr Barnier had also vowed that the withdrawal agreement "will be implemented with rigour and discipline by all sides and it cannot be reopened under the guise of implementation".
Mr Kelly said he believed that meant there could be no relaxation of "challenges" as a result of the rules governing NI in the agreement protocol.
"Those challenges are additional costs and complexities which will mean our that current supply chain and routes will be hindered - it's not the unfettered access that has been promised to us by both UK and EU in negotiations up until now."
But Mr Kelly was encouraged by Mr Barnier's vow to continue to listen to business. "We are very pleased about that and we have to make sure government in the UK gives us the same level of engagement," he said.
Mr Kelly added that with the UK leaving the EU on Friday, businesses now needed to prepare for what may await them at the end of the implementation period.
Roger Pollen, FSB NI head of external affairs, said small firms were relieved a no-deal Brexit had been avoided, but said their interests must to be taken into account.
"It is of utmost importance that the new trading relationship does not introduce administrative burdens, which will add harmful complexity and cost," he said.
"Small businesses are the very bedrock of the economy and they must be able to continue to play a full and valuable role in the UK and EU markets without restrictive barriers to trade."