This article refers to a similar document from Great Britain. Regarding those elections I had also read religious/theological documents showing that Muslims have an obligation to vote.
A French language document is circulating on the internet In Brussels calling to boycott the June 10th elections because they are "illegal", reports Le Soir.
The twelve page document is called 'Participer aux élections' (participation in the elections) and is being spread in the Arab-Muslim community in Brussels and has already appeared in various blogs.
The text is anonymous and is written "theologically" with knowledge of the issue. The Koran and the Sunnah are quoted, the author refers to various prophets and bases himself an a Fatwa in Great Britain.
According to Le Soir the document was drawn up in a Brussels mosque where Salafists come to pray. Salafism is a movement in Islam that wants to bring back the faith to its original form.
The document states that only Allah has to right to issue absolute laws. "Any Muslim who takes part in the elections is an apostate," it says.
Source: HLN (Dutch), Le Soir (French)