The EU will make vaccine companies respect their delivery agreements, European Council President Charles Michel said on Sunday.
"We intend to make the pharmaceutical companies respect the contracts they signed (…) by legal means," Michel told a joint interview to French media outlets Europe 1, CNEWS, and Les Echos.
"We will see if we need to roll up our sleeves and fight for reasons explaining the delays," he said, pointing out that the bloc wants "transparent dialogue" from the vaccine producers.
Biotechnological firm Pfizer/BioNTech announced last week that it would temporarily slow down vaccine shipments to Europe. The company explained the delays by a decision to reshuffle capacities to boost long-term production.
On Friday, AstraZeneca also promised to deliver smaller quantities then initially agreed because of "reduced yields at a manufacturing site".
But the shipments have not even started because the European Medicine Agency is expected to approve the company's jabs next week.
The EU, which has a population of 450 million, made agreements with six vaccine producers -- Pfizer/BioNTech, Moderna, AstraZeneca, CureVac, Johnson&Johnson, and Sanofi/GlaxoSmithKline -- to buy about 2.3 billion vaccine doses.
In a new strategy revealed on Tuesday, the European Commission suggested EU member states to speed up the vaccination campaigns to immunize at least 70% of the adult population by summer.