Buying things online from the UK could get a lot more expensive if there's a no-deal Brexit.
Returning items bought online could also be more difficult if the UK crashes out without a deal.
The Government has also warned consumers might not have all the protections they would usually have if buying from the UK.
Tánaiste Simon Coveney says it is one of the many risks of no-deal Brexit.
He said people buying from the UK in the event of a no-deal Brexit is "the equivalent of buying product from a third country outside of the European Union, outside of our single market, where tariffs may apply, where diffierent tax rates may apply.
"And so I think you will see a real change in online traffic as a result of that."
Meanwhile, the Government and officials have for the first time warned about the prospect of checks on goods crossing the Northern Irish border and the end of frictionless trade in the event of a disorderly Brexit.
Mr Coveney said “some action somewhere in the economy” would be necessary to protect the EU’s single market, and ensure Ireland is “not forced out” of the bloc’s trading area.