He is suing for unspecified damages for violation of his civil rights.
Barneys, in a statement this week, said that while the store ordinarily does not comment on pending litigation, it was making an exception in this case.
"After carefully reviewing the incident of last April, it is clear that no employee of Barneys New York was involved in the pursuit of any action with the individual other than the sale," the statement said. "Barney's New York has zero tolerance for any form of discrimination and we stand by our long history in support of all human rights. We are very sorry that any customer of our store would have this experience."
An NYPD spokesman told ABC News that the department was investigating the incident, including whether the officers had acted on their own initiative or in response to a request from Barneys.
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Barneys CEO Mark Lee, in a later statement, said the store was conducting a thorough review of its practices, "to ensure that they reflect our continued commitment to fairness and equality."
He said the store had retained civil rights expert Michael Yaki, who serves on the U.S. Commission on Civil Rights, to assist the store in its review.
"Mr. Yaki will be provided with unrestricted access to all aspect of our store operations," Lee said.
Yaki, in a statement released Friday by Barneys, confirmed he had been retained by the store.
The second incident allegedly occurred in February after Kayla Phillips of Brooklyn, 21, had purchased a $2,500 Celine handbag, according to the New York Daily News. The News reported that she, like Christian, was detained and questioned. She did not come forth with her accusation until this week.
Phillips has not filed suit, but she has filed notice of her intention to sue. Barneys, asked about Phillips' accusations, directed ABC News to the store's previous two statements.