The unions and construction employers were unable to reach an agreement in a negotiating blitz that was cut short over the weekend.
The unions walked away from the bargaining table Saturday.
Workers insist a main problem for them was an attempt by the Quebec construction association to change the amount of overtime they would get for extra hours worked.
The union also says they were being asked to agree to a 14-hour day and six-day work week at regular wages.
The strike will affect both residential and commercial construction sites, including the two super hospitals in Montreal.
A spokesperson for the employer's groups says the ball is in the unions' court since they were the ones who broke off talks. The strike also affects Target stores under construction in the province.