Northern Ireland would become a backwater
Over 30% of sales at The Rug House in Newry - which has both a website and a physical store - are EU exports, its managing director Paul Vallely has said.
And he said he feared a Brexit could cost the company as much as £1m in sales.
He said: "As recently as 18 months ago I would have said that it was impossible for [the UK to leave the EU] but given the migration tint to the discussions, for the first time we are getting very worried that it might happen.
"If the UK leaves the EU, Newry would become a backwater town again, it'd be a dead end. We need to remain part of the north-south corridor."
Mr Vallely said it was important that business owners spoke to members of the public about how an EU exit would affect them.
He said: "Most people vote with their heart and not their head. It's important that they hear real stories and know about the impact it would have on the town. Businesses need to point out the problems with an exit.
"Everyone from hoteliers to mechanics - most if not all of them here - see the problems we would face in Newry if the UK were to leave the EU.
"It's hard to find many right thinking people who support Brexit. It's not something even worth thinking about here.
"People in England don't seem to realise the full implications of an 'out' vote for businesses so it's important our politicians make themselves heard and speak effectively at Westminster. We're the only part of the UK with an EU border so it's going to affect us worst here."
The Rug House, which is based in Carnbane Way, was founded by Paul and his sister Clare.
The pair made contacts with factories in mainland Europe and started ordering directly from manufacturers. The business continued to grow and currently employs just under 30 people.