WASHINGTON, Jan 8 (Reuters) - A federal judge on Tuesday denied a request by mechanics at UAL Corp.'s (UAL) United Airlines to immediately block the work of a White House panel that has prevented the workers from striking. U.S. District Court Judge James Robertson instead set a further hearing for Friday on whether the establishment of a presidential emergency board was justified. "The application for a temporary restraining order does not demonstrate that an immediate threat of irreparable injury exists," Robertson said in declining to halt the emergency panel's work. The International Association of Machinists and Aerospace Workers has argued there was no justification for appointing an emergency board as a strike would not have substantially interrupted interstate commerce.