The European Union is ready to start withholding COVID-19 shots from the U.K., risking a sharp deterioration in relations with London in a bid to turn around its lackluster vaccination campaign.

The EU will start reviewing, and likely rejecting, export authorization of AstraZeneca PLC coronavirus vaccines to the U.K. until the drugmaker fulfills its delivery obligations to the 27-nation bloc, according to a senior EU official.

The EU has contracts with the company that aren’t being respected, and any vaccines and ingredients produced in European factories will be reserved for local deliveries, said the official, who asked not to be named because the decisions are under consideration and haven’t been made public.