The Act respecting elections and referendums in municipalities dates from 1987. So it has certainly been in the law since then. Before that, municipal elections and referendums were governed by various statutes, including the Charter of the City of Québec, the Charter of the City of Montréal, the Cities and Towns Act and the Municipal Code. They all laid down different rules. It was all completely reformed in 1987. The act now applies to all municipalities in Quebec.
On December 1st, 2009. See this statement in context.