Return of checks could hit relationship with our most important export partner
Our new life outside Europe... your guide to how things are likely to change
Cross-border trade could become more complicated following the UK's historic vote to leave the EU.
Seamus Leheny, head of the Freight Transport Association in Northern Ireland, said the importance of the sale of goods between businesses and consumers on either side of the border "must not be forgotten" when Brexit negotiations begin.
More than a third of Northern Ireland's trade in goods and services is with the Republic, making it our biggest export partner.
There is also a daily movement back and forward of large parts of the population of either side of the border.
According to research by the Northern Ireland Statistics and Research Agency and the Republic's 2011 Census, that year there were 6,456 Northern Ireland people working in the Republic, and 8,295 southern Irish people working in Northern Ireland.
The border between Northern Ireland and the Republic is set to become the only land border between the UK and in EU.
Mr Leheny said that leaving the EU risked new costs, restrictions and paperwork on goods coming in and out of Europe. "Northern Ireland has enjoyed arrangements with its neighbour for almost 100 years for free movement, commercial, legal and social matters," he added.
"The UK is Ireland's largest mutual trading partner, and this relationship must be maintained through the Brexit negotiations."
Stephen Kelly, chief executive of lobby group Manufacturing NI, said he believed a hard border had already returned in the minds of manufacturers, with concerned firms holding back on investment plans. "It's clear that for some that the border is already back, regardless of any future trade, tariff and freedom of movement agreement," he added. "Capital and investment is already being locked out."
Danske Bank chief economist Angela McGowan said that Northern Ireland would need "a trade deal that keeps the UK as close to the EU as we can possibly get". "A deal that leaves us economically isolated from Europe would have massive consequences," she explained.
Employment lawyer Louise McAloon from Worthingtons Solicitors said there would be uncertainty for border areas.
"The bigger issue is how the departure from the EU may affect people's lives in terms of increased times for commuters, the inconvenience of multiple checks on short journeys to the shops or visiting friends and family, and the potential detriment for cross-border trade and investment," she added.
"Everyone will be hoping that pragmatic discussions and negotiations can avoid the imposition of physical border controls, something which I'm sure everyone believed had been consigned to the history books."