Health Commissioner Stella Kyriakides said the EU “will take any action required to protect its citizens”.
Last week, AstraZeneca told the EU it was falling behind on its supply target because of production problems.
The EU has been criticised for the slow rollout of the vaccines, which it buys on behalf of all member states.
The row could also affect supplies to the UK of the Pfizer-BioNTech vaccine developed by the US and Germany. Pfizer’s Belgian plant supplies the UK.
The UK government said it was in “close contact” with vaccine suppliers.
“Our vaccine supply and scheduled deliveries will fully support offering the first dose to all four priority groups by 15 February,” a government spokeswoman said.
Inoculation programmes in some EU members have already been slowed due to a cut in deliveries of the Pfizer-BioNTech vaccine, with some nations threatening legal action.
Ms Kyriakides tweeted that Monday’s talks with AstraZeneca “resulted in dissatisfaction with the lack of clarity and insufficient explanations”.
“EU member states are united: vaccine developers have societal and contractual responsibilities they need to uphold”.
Ms Kyriakides said the EU had requested “a detailed planning of vaccine deliveries”, and the next meeting with AstraZeneca would be held on Wednesday.
The health commissioner warned that “in the future, all companies producing vaccines against Covid-19 in the EU will have to provide early notification whenever they want to export vaccines to third countries”.
AstraZeneca has so far made no public comments on the latest developments. (Courtesy BBC)