UK citizens may need to apply for visas if they wish to travel to EU countries after Britain formally leaves the organisation.
Officials at the EU's executive body are considering plans that would mean British business travellers and tourists would need to apply online for a visa and pay a fee before travelling to the continent, Sky News reported.
This would be a similar structure to the US's current visa programme, called the Electronic System for Travel Authorisation (ESTA), under which citizens from countries including the UK, Australia, Japan and France can obtain a visa waiver by paying a fee and filling out pre-trip documents online.
Read more: What now? The UK and the EU Single Market
At present, British travellers require a passport to travel throughout other EU member states, but do not have to apply for short-term visas.
More details about the EU's Travel Information and Authorisation Scheme (ETIAS) are expected to be published later this year, while speculation about the content of Brexit negotiations is ongoing and Article 50 has yet to be invoked.
Addressing the House of Commons on Wednesday, May stayed tight-lipped on Brexit talks, saying she would not provide commentary on discussions, despite pressure from MPs to clarify the government's stance on Single Market membership.