Rebelo de Sousa emphasised that the new law would give enormous prerogatives to doctors to decide who would be euthanised or not.
A number of groups, even Palliative Care groups, have called the proposed legislation from the far left "deeply flawed".
Spanish bishops call for "a genuine therapeutic alliance (...) to humanise the death process through material and spiritual help"
"It is shocking to think that more than sixty-two million Americans have lost their lives in the womb since 1973," he wrote.
They called on the Head of State to veto the newly enacted legislation as "contrary to the foundations of the constitution."
Over 95,000 people signed a petition demanding the project of law to be rejected.
At the moment, Belgium, Luxembourg and the Netherlands are the only European countries where euthanasia is permitted.
Netherlands is among the most liberal countries in the world when it comes to the question of assisted suicide.
The rule says it's not necessary for the doctor to agree with the patient the time or manner in which euthanasia will be given.