Ingrid Lewis-Martin, chief adviser to the mayor, had her phone seized upon return to the United States from a vacation in Japan, her attorney said.
Investigators also searched her Brooklyn home, sources told ABC News.
Multiple agencies are interested in Lewis-Martin, including the Manhattan District Attorney's Office and the Southern District of New York, the same prosecutor's office that charged the mayor with bribery, solicitation, and fraud.
The Manhattan District Attorney's Office's interest in Lewis-Martin appears to stem from their indictment last year of former Buildings Commissioner Eric Ulrich for taking bribes.
Spokespeople for both offices declined to comment.
Her attorney, Arthur Aidala, issued the below statement:
"Ingrid Lewis Martin has been served with a subpoena from the Southern District of New York and her phones were given to the New York County District Attorney's Office. She will cooperate fully with any and all investigations and Ms. Lewis is not the target of any case of which we are aware."
Lewis-Martin is a longtime friend of the mayor and one of his closest aides. She was a fixture at his weekly news conferences, sitting next to him until the last two weeks.
The mayor addressed her absence at this week's Q&A, where he said she was on "a long needed vacation" in Japan.
"I am hoping she's having fun. And I am not annoying her at all. And when she texts me, I say, 'Ingrid, enjoy your vacation. We got this,'" he said.
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