Portugal's Constitutional Court has overturned a law decriminalising euthanasia, saying the legislation is too imprecise.
The bill was passed by the Portuguese parliament in January.
It allows euthanasia and medically-assisted suicide for terminally ill and gravely injured people.
Last month, the country's President Marcelo Rebelo de Sousa asked the court to evaluate the law before his approval, saying that the legislation could create legal uncertainty.
On Monday, seven out of twelve judges agreed the bill lacked "the necessary rigour" and rejected it.
The court stated that the proposed law is imprecise in identifying the circumstances under which assisted suicide procedures can occur and what defined a person in "extreme suffering".
The rules on when euthanasia can be granted must be "clear, precise, clearly envisioned and controllable", the judges added.
However, the court denied that the right to life was "an insurmountable obstacle" for the law to pass.
"The right to life cannot be transfigured into a duty to live under any circumstances," said the president of the court, João Pedro Caupers.
The governing Socialist Party, which has supported the bill, now has the chance to re-word the legislation before voting to pass the bill once again.
MP Isabel Moreira said the Constitutional Court's comments on euthanasia were "a great victory for civilisation".
If approved and passed, Portugal would become just the fourth country in Europe to legalise euthanasia after Belgium, the Netherlands, and Luxembourg.
Right-wing parties in Portugal have criticised the law, in the midst of a tense debate on the appropriateness of the bill's timing due to the COVID-19 pandemic.