The union says the employer rejected a conciliator's proposal Monday evening.
Union executive director Serge Cadieux said the commission's decision was "irresponsible and would cause a lot of harm to the construction industry."
He added that the conciliator's proposal respected the financial framework imposed by the Treasury Board and accepted by all public and parapublic sectors. The settlement also included adjustments to the pension plan to balance costs and permit a profit without increasing contributions by the commission and employees.
Members of Local 573 last week rejected by 86 per cent the commission's last contract offer and voted in favour of a strike. Employees have been without a contract since December 2009.
The commission responded by approving a two-day lockout last Thursday over the unwillingness of the union to negotiate in good faith the renewal of the collective agreement. The work stoppage would allow it to prepare for the general strike.
Since May 7, the Quebec Construction Commission has faced intermittent strikes and four days of a general strike.
Three hundred investigators will continue with their activities throughout the labour dispute.
Picketing will start today at regional offices of the commission across Quebec.