Air samples taken underground at the Second Avenue subway construction site turned up high levels of a dangerous dust particle known to cause lung cancer.
The Occupational Safety and Health Administration found silica particles more than three times the acceptable level at East 69th Street in November.
The test results were released to State Assemblyman Micah Kellner last week.
Silica gets kicked up during construction, and can lead to a chronic lung disease called silicosis.
The Metropolitan Transportation Authority says the dust levels shown in the preliminary findings do not impact street-level air quality, because silica drops to the ground instead of floating in the air.
Schiavone Shea Kiewit (SSK) Constructors, the three joint contractors hired by the MTA to work on the Second Avenue subway lines, said in a statement that the company is reviewing the citation and takes the health and safety of their workers very seriously.