The European Commission has imposed tough new export controls on drugs that can be used to execute people in the United States.
Some of the drugs, which are in short supply in the United States, are legally required for lethal injections in the 34 American states where the death penalty is still used.
European companies wanting to export drugs such as the sedative sodium thiopental now have to ensure the product is not going to be used for executions.
The BBC reports the ruling could slow the rate of executions in the US.
The death penalty is banned by all 27 members of the EU, which wants it abolished worldwide.
Sodium thiopental - the first of three drugs used for executions - is intended to make the condemned person unconscious before deadly drugs are administered.
Earlier this year, Hospira, the only manufacturer in the US, stopped making it.
The BBC reports the shortage has already led to a marked drop in the number of US executions.