He joined the right-wing populist party Pim Fortuyn List (LPF) on 6 May 2002, the day Pim Fortuyn was assassinated, and became a board member of its South Holland chapter. He left the board later that year and joined the splinter party Democratisch Platform Nederland. De Vree also served as spokesperson for Actiecomité OZB Nee (Action committee property tax no), that was founded in 2004 after his municipality, Hardinxveld-Giessendam, had announced it would raise its property tax by 85%. As a result of the backlash, the municipal council lowered the increase to 55%.