Turkish President Recep Tayyip Erdoğan filed a criminal complaint against Dutch far-right leader Geert Wilders with Turkish authorities Tuesday. In his complaint, Erdoğan alleges that Wilders insulted him on social media.

Since assuming office in 2014, Erdoğan has consistently sued people over alleged insults, and thousands have been convicted. In Turkey, insulting the president carries a four-year prison sentence.

Wilders, a leading far-right leader in Europe, posted a cartoon of Erdoğan with the caption “terrorist” on Saturday. On Monday he shared an illustration of a sinking ship with a Turkish flag and a caption promoting the removal of Turkey from NATO. In response, Erdoğan filed the lawsuit. His lawyers argue that because the insults were directed at Turkey’s president, the matter falls within Turkey’s jurisdiction. They claimed the insults are not protected under the freedom of expression.

Erdoğan’s lawsuit is familiar territory for Wilders. In 2011 he was acquitted in a hate speech trial for comparing Islam to Nazism and advocating for banning the Koran. Last month, an appeals court acquitted him of discrimination, while upholding a conviction for intentionally insulting Moroccans. He has also called for taxing the hijab. As a result of death threats following his anti-Islam rhetoric, he has spent 16 years living under tight security.

Dutch Prime Minister Mark Rutte called the lawsuit unacceptable and an infringement of the freedom of speech. He added that a legal case that could result in a curtailment of the freedom of expression was unacceptable, and that he plans on raising the issue with Turkey.