The mandatory grounds for refusal are basically the following: a)certificate is incomplete, b) an eventual breach the principle of ne bis in idem, c) there is an immunity of the defendant that under Portuguese law that would prevent the execution of the decision, d) the person subject to the decision would not be be charged in Portugal by reason of age, e) the person concerned has not been informed personally or through a representative, of his or her right to contest the case and of the time limits for appeal, f) trial in absentia, except if : the person concerned was summoned of the scheduled date, or if it may be unequivocally established that the person was informed that a decision would be handed down in his/her absence, if the person was summoned of the trial and was represented by a counsellor, or if after being served with the sentence, the person has a right to a re-trial.
The optional grounds for refusal are the following: a) The facts under investigation are not punished under portuguese law (with the exception of the offences mentioned in article 5 of the FD, that won´t be verified on double criminality) b) the proceedings are statute-barred under the internal law, and Portugal has jurisdiction over the facts, c) the financial penalty is less than 70 euros, d)fundamental legal principles as enshrined in Article 6 of the Treaty on European Union have not been respected.