A grand jury in Pennsylvania is to go into session tomorrow consider allegations that Wal-Mart used illegal workers to clean floors at its stores. Assistant Attorney Wayne Samuelson won`t discuss details of the case, but says the grand jury is scheduled to meet. He says the investigation will be a long one. Grand juries meet in secret and can hand up indictments. Wal-Mart spokeswoman Mona Williams said Wednesday that the company is bound by federal rules surrounding grand jury secrecy and could not comment. Earlier, the company acknowledged it was the target of the investigation. Janitorial companies hired by Wal-Mart were at the center of a 21-state sweep of 60 Wal-Mart stores on October 23rd. About 250 workers from 18 different countries were arrested, and ten of them were employed by Wal-Mart itself.