Amazon has warned shoppers in the Republic that they could face VAT and import fees once Brexit kicks in on January 1.
Shoppers who order from Amazon.co.uk but whose packages are delivered to a European Union address can expect to pay more once the Brexit transition period ends.
The change will mean higher prices for shoppers in the Republic.
Amazon does not have a site specific to the Republic so many shoppers buy from the UK site.
There are also fears that the supply of some goods to Northern Ireland may be hit due to confusion amongst producers and retailers.
Although a last-minute Brexit deal on border checks was agreed on Monday, some businesses have already said it is too late for them to prepare for any changes come January 1.
Ulster Unionist leader Steve Aiken has already warned that the Northern Ireland protocol, which will see the north continue to enforce the European Union's customs rules and remain within the single market in goods, could see checks on goods bought online.
Mr Aiken also said goods transported from Britain could increase in cost.
Amazon said it will continue to accept returns for damaged, defective or incorrect items bought from Amazon.co.uk and posted to an EU address.
But it said that for other returns, customers will have to pay transport costs and any import or customs fees.
