Businesses need more information on where checks on animals and goods might be carried out in the event of a no-deal Brexit, according to Chartered Accountants Ireland.
The Government indicated last week that if checks were required, they may be carried out away from the border.
Cróna Clohissey, of Chartered Accountants Ireland, said it was a huge issue for businesses, particularly those operating in the border region.
"There's not a whole lot of information filtering through. The Government has made clear that there won't be any border infrastructure.
"Ireland is in the EU Single Market. It has to protect the EU border. Whether checks take place in designated depots, warehouses or places away from the border, there has to be clarity," MS Clohissey urged.
She also pointed to issues around safety regulations that had to be adhered to that necessitated a flow of information to businesses.
"Truck drivers need to know where they need to drive to. There are regulations around hourly allowances in terms of how much you can drive, routes you need to take. This is going to cause supply chain disruption. Businesses need to plan for that now."
Revenue released figures yesterday showing that more businesses had sought a customs registration, the most basic requirement for trading with the UK post-Brexit.
However, many thousands of businesses have still to do that.
"That's the absolute minimum you need to import or export to and from Britain. The larger traders have sorted themselves out. It's the smaller guys that haven't and these are the ones that will be most affected.
"The EORI is the minimum. It takes three minutes to register and it has to be done now."
After the EORI, Cróna Clohissey said putting in place preparations around customs administration was the second step for businesses.
"They're not sure what returns need to be filed or whether they need to file returns. Regardless of whether there's a deal or not, returns will have to be filed. Get onto revenue.ie, have a look and see what needs to be done," she advised.
Around tariffs, Ms Clohissey said CAI had taken calls from businesses that don't even know where to look to find out what tariffs might apply to their goods in the event of a hard Brexit.
"If you take a case where you're going to be importing machinery from the UK, you could be looking at a tariff of 15%. That's a huge extra cost in terms of your product becoming much more expensive to import."
She suggested going onto the EU TARIC database to check what tariffs night apply as this is an issue that could have a direct impact on cash flow.