The MTA says the accident happened around 9:30 a.m. at the Mineola Station.
Contractors were constructing a pedestrian bridge when a crane came in contact with a high voltage line.
"The contact with the high voltage line created an arc to the bridge that seriously injured a female ironworker who was on the structure at the time," MTA Construction and Development President Janno Lieber said in a statement.
The woman was taken to the hospital and is in critical condition.
The MTA says all work on the project has stopped pending an investigation.
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