Construction workers at the new CHUM superhospital site in downtown Montreal walked off the job Wednesday morning to protest working conditions.

More than 1,000 workers put their tools down and gathered on the street outside around 8:30 a.m.

They returned to work about three hours later after officials gave them assurances that the hospital's air conditioning system would be running by next Monday.

"All the members are going back to work to show good faith," said union representative Sami Saba.

Workers said they wanted the windows open or a ventilation system installed to help with air circulation in the building, especially on its upper floors.

The hospital gave the workers permission to remove their safety vests as a temporary measure.

Air quality tests conducted on June 7 came back normal, but it was recommended that further tests be carried out in warmer weather.

The workers' union said it may conduct its own test to measure air quality during a heat wave.

A high of 30 C is expected today with a humidex reading of 36.

The completion of CHUM, which is being built by a public-private partnership, has been delayed by five to seven months.

It was initially slated to be finished in April. Construction is now expected to wrap up in the fall.