A Brooklyn man has said that he will refuse to testify before a federal grand jury that is believed to be looking into the explosion of a homemade bomb in Times Square in 2008, setting the stage for a confrontation that could send him to jail for contempt of court.

A lawyer for the man, Gerald Koch, said that he had been subpoenaed as a witness and granted immunity, but that he was not a suspect in the bombing, which took place outside an armed forces recruitment center in the middle of the night and caused no injuries. Mr. Koch said in a written statement late last week that in 2009 he had been called before a previous grand jury investigating the case, but did not testify because he knew nothing about what happened.

“I will once again refuse to testify to the federal grand jury in ethical resistance to participation in a fruitless exercise of fear-mongering and government intimidation,” Mr. Koch wrote.

He noted that he could be jailed for up to 18 months, and added: “I accept this recompense, understanding that in doing so I will reinforce a tradition of defending individual rights in the face of state repression.”