Certainly one Belgian lawyer has already stated that he thinks the EU Commission don't have a leg to stand on here. Not that I expect that to slow them down.
https://twitter.com/JeremyC64/status/1355156181753475073?s=1...
Awkwardly it seems Pfizer might shift to supplying the UK from the US and the UK seem content that they have no contractual need to share the AZ doses from the UK facility. So the EU don't seem to have any leverage on this issue.
Some have tried to say this debate is EU vs AZ but this map suggests otherwise.