Each year a different Dutch city or town is chosen to host the arrival, by boat, of the saint and his sidekick. For years Dutch actor, Stefan de Walle, has played the character at the arrival ceremonies.
But Black Pete, whose character is usually performed by an adult with a blacked-up face, wearing an afro wig, gaudy costume and red lips, has increasingly come under fire for being a racist stereotype.
Now police are probing an online threat posted last year on Facebook by an extreme leftwing group, named De Grauwe Eeuw by Dutch media, which is opposed to Black Pete.
The group specifically mentioned de Walle, and called for "a price to be put on Sinterklaas' head. Without a doubt (he must be) dead," the daily De Telegraaf said.
The price should double "if it happens during his national arrival so it can be witnessed by all the children, who should be covered by his brains and bone splinters," the message said, according to De Telegraaf, before it was removed shortly afterwards.
"Then we'll forever be rid of the festival -- and of that irritating... actor that portrays Sinterklaas," the post said.
Prosecution spokesman Ties Kortmann told AFP "police are investigating a Facebook post containing an inflammatory message."
"They have a suspect and we are waiting for the dossier before making a decision to prosecute," he added, refusing to give further details.
The group's name is a word-play on the Dutch Golden Age, meaning the "Grey Age" because of Dutch involvement in colonialism and slavery.
Dutch national anti-terror agency NCTV said in a 2017 report the group was relatively new and claim to "fight against racist and colonial symbols in Dutch society, such as Black Pete, (and) the Dutch East Indies Company".