About 350 builders working on the new terminal at Pulkovo Airport in St. Petersburg have been laid low by acute food poisoning.
Thirty-five ambulance brigades were called into action Monday to take the workers to the hospital, were 200 are still receiving treatment, Interfax reported.
Fifteen of the men are in critical condition, Fontanka.ru reported.
The poisoning may have been caused by poor quality chicken served to the men by the company they work for, Sofia, prosecutors said.
Police are checking the ingredients used to make the builder's food and have told the suppliers to suspend distribution.
Traffic police are carrying out an investigation to find out whether safety requirements for food transportation and storage were infringed.
If evidence of wrongdoing is found, the case will be handed over to the Investigative Committee.