Employers' group Ibec has warned economic growth next year could be more than halved if the UK leaves the EU without a deal.
The organisation predicted Gross Domestic Product growth this year will reach 4%, with households reaping the benefits of a highly performing economy.
But it expects that expansion will ease back to 2.7% next year as the Irish and global economies reach the top of the current economic cycle and the slowdown begins.
However, the estimates contained in its latest Quarterly Economic Outlook are predicated on there being a Brexit deal.
Ibec said that if there was a hard Brexit, it expected continued depreciation in the value of sterling, cancelled investment, falling consumer confidence, rising costs and significant trade disruption will collectively have a major impact.
In such an event, the economy will still grow, it anticipates, but that growth would be more than halved, compared to what it would be in a deal scenario.
But it said the challenge of a slowdown over the coming years would not be eliminated by a Brexit deal, as rising trade tension would lead to a more difficult environment for economies such as Ireland's.
As a result, Ibec said the Government must include extensive new State-aid supports to assist vulnerable companies in October's budget.
"2018 was the first year where the value of Irish indigenous exports fell since 2011," said Ibec Chief Economist Gerard Brady.
"This trend has been reversed in the early months of 2019 driven by continued increases in production in both the alcohol and dairy sectors.
"Both sectors will face challenges over the coming year due to US tariffs and Brexit. Ibec analysis has shown that Irish goods are the most exposed, on a per capita basis, to the proposed US tariffs on EU goods.
"Irish exports worth €818 million could be hit by new tariffs."
The report also said it was imperative that in the face of any global slowdown, the Government does not repeat the mistakes of the past by cutting productive spending.
"The best way to prepare the economy for the challenges ahead is to follow through on funding key areas of our economic infrastructure through the National Development Plan, a new national innovation strategy, and by setting out a clear plan for the funding of Higher Education," it stated.
The analysis found that while €2bn a month is being invested in the Irish economy, twice its pre-crisis peak, there has been some weakness in SME investment in recent months.
But it says this slowdown must be taken in context, however, with investment still close to record levels.
"Feedback from members suggests this slowdown is closely tied to Brexit related uncertainty," the report stated.
"In the event of a positive political breakthrough on Brexit the economy could see a significant boost to investment in 2020."