The European Union announced plans to invoke emergency rules that could substantially reduce exports to the United Kingdom and other countries for six weeks.

AstraZeneca, a central provider of vaccines to the European Union, had reduced EU projected shipments to the EU after encountering production delays at plants in Belgium and the Netherlands.

AstraZeneca will likely face the biggest impact from the rules, which would also apply to Pfizer and Moderna vaccines.

Canada and Israel also rely on EU-produced COVID-19 vaccines.

The U.S. and U.K. are largely reliant on domestically-produced vaccines.

It’s possible, however, that the EU and U.K. will come to a common agreement related to COVID-19 shipments. A joint statement released from the two governments describes an attempt to “ensure a reciprocally beneficial relationship between the UK and EU on COVID-19.”

U.K. prime minister Boris Johnson had earlier expressed frustration at the plan. “I don’t think that blockades, of either vaccines or medicines or ingredients for vaccines, are sensible, and I think that the long-term damage done by blockades can be very big,” he said.