A member of the city’s human rights commission, Omar Mohammedi, received a death threat by mail last week, demanding that he withdraw a lawsuit he filed on behalf of six imams, identified in the case as John Does, who were removed from a USAirways flight in November.

The letter threatens the commissioner as well as the six imams whom Mr. Mohammedi represents in his capacity as a private civil rights attorney.

Mr. Mohammedi, who did not return a call for comment, has alerted law enforcement officials about the threat, a spokesman for the Council on American-Islamic Relations, Ibrahim Hooper, said.

“The threat calls for the lawsuit to be ended, so it can rightly be termed a terror threat,” Mr. Hooper said of the letter. “It can be categorized as such, and law enforcement authorities should act accordingly.”

The lawsuit that prompted the threat was filed in March in federal court in Minneapolis. Mr. Mohammedi sued USAirways and passengers on the flight who may have complained to the airline about the imams. The imams attracted attention by praying at the boarding gate, switching seats once on the plane, and requesting seat belt extenders, according to news reports.

Mr. Mohammedi’s suit sparked a response in Congress, where at least two lawmakers introduced legislation to immunize passengers from being sued for reporting behavior that strikes them as suspicious.

The death threat, signed American Jihad, describes Mr. Mohammedi’s suit as “an act of supporting terroristic behavior.”

Mayor Bloomberg appointed Mr. Mohammedi to the city’s Commission on Human Rights. Mr. Mohammedi also serves as the president of the New York Chapter of CAIR.