As Europe is gripped by a third wave of coronavirus infections, tensions are mounting over its faltering vaccine programme.
EU leaders voiced frustration on Thursday at the massive shortfall in contracted deliveries of AstraZeneca's vaccine.
Of 300 million doses due to be delivered to EU countries by the end of June, Astrazeneca aims to deliver only a third.
The EU's executive is now threatening to block exports of the vaccine.
"We have to and want to explain to our European citizens that they get their fair share. And therefore the second principle is companies have to honour their contract to the European Union before they export to other regions in the world. And this is of course the case with AstraZeneca."
This week, the European Commission unveiled plans to tighten oversight of vaccine exports.
This would allow greater scope to block shipments to countries, like Britain, with higher inoculation rates.
As of March 23, Britain had administered nearly 46 shots for every 100 people, compared with under 14 per 100 in the EU.
Britain says it did a better job negotiating with manufacturers and arranging supply chains.
But the EU says it should share more, notably to help make up the shortfall in contracted deliveries of AstraZeneca shots.
EU leaders, however, are divided about how tough a stance to take.
France has made clear its fully behind blocking exports, but the Netherlands and Germany have been more cautious.
German Chancellor Angela Merkel said the EU must respect global supply chains and fight protectionism.
While, Dutch Prime Minister Mark Rutte warned of "broader consequences" if the bloc followed through on its threats.