They're asking Quebec's minister of transportation, Robert Poëti, to send a clear message that the project is a priority.
Laval Mayor Marc Demers said citizens have waited 40 years for the project to be realized.
He said the completion would decrease congestion, reduce air pollution and help with economic development. He said it would also help reduce traffic on other congested highways, such as Highway 15.
Montreal Mayor Denis Coderre, on an official visit in Paris, appeared by video link to support Demers and his fellow municipal leaders.
The proposed $600-million project would see Highway19 expanded to a full four lanes from the island of Montreal all the way to Highway 640 in Lanaudière, north of Laval.
Critics – including environmental groups and Montreal's official opposition, Projet Montréal – have denounced the planned expansion as a costly mistake.
Projet Montréal Councillor Craig Sauve has said it would bring more cars onto the island of Montreal and the Ahuntsic-Cartierville borough in particular.