Belgian federal prosecutors on Wednesday objected to a court ruling undermining the PKK's designation as a terrorist group.
The objection came after an appeals court last month upheld a ruling which said PKK activities in Europe could not be classified as terrorism.
A local court in November last year had refused the federal prosecutor's request to send 36 alleged PKK members to a higher criminal court, claiming an "armed campaign cannot be considered terrorist acts."
The ruling was made despite the PKK being listed as a terrorist organization by the EU, the U.S. and Turkey.
In response to last month's decision, Turkey said the Belgian ruling was a yet another example of support for terrorist groups seeking to harm Turkey's security and interests.
The Turkish foreign ministry in a statement said the decision "reveals once again the fact that Belgium is a weak link in countering terrorism in Europe and in the world."
"Turkey will also intervene as a third party in the appeal process against this unacceptable ruling," it added.
Turkey and the federal prosecutor's office have two months to put their arguments to Belgium's highest court. It is expected that the court will decide within a year.
The suspects are accused of kidnapping children from their families in Belgium and European countries, and sending them to Greece and Iraq for training.
They are also accused of forging documents and extorting businessmen.
Among those standing trial are Remzi Kartal and Zübeyir Aydar, accused of being senior members of the PKK's European network. They were among PKK suspects arrested in March 2010 in raids on 18 addresses across Belgium.
The court case began in October 2015 following an investigation that began in 2006.
Belgium has been criticized in the past for failing to act against the PKK.
In August last year, the movement's supporters in Brussels were allowed to celebrate the anniversary of the terror group's first attack in 1984.
Five months earlier PKK sympathizers had been allowed to set up tents outside EU buildings ahead of a Turkey-EU summit.
For more than 30 years, the PKK has waged a terror campaign against Turkey leading to the deaths of more than 40,000 people -- security forces and civilians alike -- including more than 1,200 since July 2015 alone.