The founder of a Muslim charity in the United States was called before a federal grand jury in Chicago Thursday. Rabih Haddad has been in federal custody since his arrest two months ago, but his lawyers say the government has not yet filed any charges against him.

Rabih Haddad is the founder of the suburban Chicago-based Global Relief Foundation. On December 14, he was arrested at his home in Ann Arbor, Michigan. At the time, the government said Mr. Haddad had overstayed his visa. In Chicago Thursday, his lawyer Ashraf Nubani said his client has been in custody ever since, but no charges have been filed against him. "He is being held in solitary confinement, meaning 23-hour lockdown in a cell that is about six foot [two meters] by nine-foot [three-meters]," he said.

Mr. Haddad was moved to the federal jail in Chicago several weeks ago. He was called before a federal grand jury on Thursday, though Mr. Nubani says he didn't know how to prepare his client for the appearance because the government had not told him what it was investigating. Mr. Nubani says he assumes the grand jury is looking into the Global Relief Foundation's operation.

The same day Mr. Haddad was arrested, the government also shut down Global Relief's offices in the Chicago suburb of Bridgeview. The government has also frozen the charity's assets while it investigates whether the organization funnels donations to terrorist groups. According to Global Relief attorney Roger Simmons, it does not. "All this charity has ever done is raise money, deliver goods to people who are in need of food, medical care, basic education," said Mr. Simmons.

Federal officials are declining to comment on Mr. Haddad's case, other than to confirm he is in custody. Mr. Haddad had three deportation hearings in Detroit before being moved to Chicago. All of those hearings were closed to his family, the public and the media. On Thursday, lawyer Ashraf Nubani filed a lawsuit seeking to have future deportation hearings held in open court. "Rabih Haddad is a great example of what happens when there are abuses of the government against our civil rights," he said. "The loss of civil rights for one means the loss of civil rights for all."

The federal government also wants to deport Mr. Haddad's wife and three of their four children, also for overstaying their visas. Their next hearing is scheduled for April 10.