The subpoena capped Tuesday's wrangling between National Transportation Safety Board officials and the attorney for Capt. Michael Gansas, who canceled a scheduled NTSB interview without public explanation.
Gansas' attorney, Catherine Foti, confirmed that she had received the subpoena but did not comment further. It calls for Gansas to appear before NTSB investigators Wednesday.
Richard Smith, the assistant captain piloting the ferry when it plowed into a maintenance pier last week, is in critical condition and still unable to talk after attempting suicide, according to his attorney.
The captain's whereabouts are considered a vital element of the investigation. City regulations require the captain to be in the ferry's pilot house during docking, which could have provided backup if the pilot was stricken.
"I think the crux of this investigation is going to hinge upon the information provided by the two captains," said state Rep. Vito Fossella, who represents Staten Island, "and that has yet to take place."
Gansas told police immediately after the accident that he was in the pilot house and that he tried to pull Smith off the controls after he lost consciousness, an official familiar with the investigation told The Associated Press.
At least one deckhand has told investigators that Gansas was not in the pilot house, the official said on condition of anonymity.
The deckhand's account was questioned by Gansas, who said the crew member was not in a position to see anyone in the pilot house, the official said.
The NTSB has interviewed 37 people, including three deckhands, spokesman Keith Holloway said Tuesday. He did not provide details of the interviews.
The president of the union representing Staten Island ferry deckhands said that he had spoken Tuesday afternoon with four crew members who were on the ferry. All had been interviewed by the NTSB, and none had been in a position to see Gansas immediately before or during the accident, said Charlie Chillemi, president of United Marine Division Local 333.
"They were down on deck doing other things," Chillemi said.
Alcohol and drug tests of the crew came back negative, and some investigators have speculated that Smith's blood pressure medication may have caused him to lose consciousness.
By Michael Weissenstein