It's the Flemish Government that introduced the requirement that has been adopted in 69 municipalities near Brussels and the language border that cuts Belgium in two.
Flemish legislation called 'Living in Your Own Area' offers municipalities the right to give priority to people with local ties when building land is sold.
Members of the FDF party that sticks up for Francophones have taken the matter to Belgium's Constitutional Court as has the Property Owners Association. The Court then sought advice from the European Court of Justice.
Ján Mazák, the Advocate General of this Court, has now finalised his advice. He says that the requirement forms an infringement of the fundamental liberties of the EU. The requirement means that some people are not able to buy or rent a house for nine years.
The European Court's advice is not binding, but generally Belgium's Constitutional Court will follow it.
In addition to the Flemish legislation many municipalities also set conditions of their own on people buying a house or applying for social housing.