Since his resignation earlier this month, former mayor Gérald Tremblay's party has lost about a dozen members. Two weeks ago, a spate of departures cost the party its majority status at City Hall.
The latest defectors include Île-Bizard-Sainte-Geneviève Mayor Richard Belanger and four borough councillors: Eric Dugas, Diane Gibb, Christopher Little and François Robert.
Belanger says the allegations of corruption made against Union Montréal over the past several weeks pushed him and his councillors to leave.
A Union Montreal spokeswoman said the departures were not a surprise, and did not comment further.
Saint-Michel councillor Frantz Benjamin was the first Union Montréal member to announce his departure last month. Councillors Alain Tassé, Frank Venneri, Lionel Perez, Susan Clarke, Ginette Marotte and Christian Dubois followed shortly afterwards.
Union Montréal Leader Marvin Rotrand announced his departure from the party on Nov. 15.None of the members have joined other municipal parties. They currently sit as independents.