The nomination of Edward Zammit Lewis as a Judge at the General Court of the EU is a "perversion of justice", the PN said on Wednesday.
They were reacting to reports that he has been confirmed as the government's nominee and is expected to face a grilling in Luxembourg in October.
Reports that Zammit Lewis would be nominated as an EU judge first circulated in June, with the PN and civil society similarly reacting negatively to the choice.
In a statement signed by Shadow Justice Minister Karol Aquilina, the PN said it was unacceptable for the government to send a person who is a close friend of Yorgen Fenech, who has been charged with orchestrating the assassination of Daphne Caruana Galizia.
"The nomination of Edward Zammit Lewis to serve as a Judge at the General Court of the European Union is a perversion of justice and unequivocal proof that Robert Abela's Government does not care about the national interest and is solely focused on serving the partisan interests of the Labour Party and its inner circle," Aquilina said.
"It is unacceptable that, out of all the individuals who expressed interest in this role, the only person chosen was someone who was part of a government condemned by three judges for creating a climate of impunity that led to the assassination of journalist Daphne Caruana Galizia."
Zammit Lewis exchanged hundreds of WhatsApp messages with Fenech even after he was revealed to be the owner of the secret offshore company 17-Black.
Author and blogger Mark Camilleri later published a transcript of the chats exchanged between the two.
The PN said that Zammit Lewis' nomination will cause further damage to the country's reputation, but Prime Minister Robert Abela is insisting on "persisting on its path of poor governance".
"This decision further confirms what Zammit Lewis himself once wrote about the leadership of our country by a Labour Government: 'Tfal u pożi…zero political competence.' The tragedy is that no one is suffering from this irresponsible form of leadership other than the Maltese and Gozitan people," Aquilina said.
He added that the PN will continue to insist that people nominated to serve in high positions in the EU should be based on merit and competence and not political convenience.
Civil society group Repubblika also expressed displeasure at the government's persistence with Zammit Lewis' nomination.
They said that during his time as minister Zammit Lewis was in "unacceptable" contact with Fewnech during a time when it was reasonable to suspect that Fenech tried to corrupt government ministers.
It was a "secret and compromising" friendship with a person who was eventually accused of killing a journalist who was close to uncovering the corruption he was involved in, they said.
"With his nomination, the government is showing how it has learned nothing and that it believes that corruption in public life is excusable if the corrupt ones are from the same tribe," the group said.
"We hope that Yorgen Fenech's past is examined thoroughly by the people who must decide on the objectionable nomination pushed by the government."