The European Union has introduced tighter rules on exports of coronavirus vaccines that could hit shipments to nations like the United Kingdom amid a deepening dispute with drugmaker AstraZeneca over supplies of potentially lifesaving shots.

The measure created an outcry Friday in Northern Ireland and the UK, amid fears it would trigger controls on vaccines shipments produced in the 27-nation bloc to the small territory that is part of United Kingdom and borders the EU’s Ireland. Under the post-Brexit deal, EU products should still be able to travel unhindered from the bloc to Northern Ireland.

The EU later made clear it won't introduce controls on vaccines to Northern Ireland.