These exceptions, taken from an article on t-g.com, include: "When the national security is at imminent harm; when death or significant bodily harm could be caused if the information is not disclosed; when significant trade secrets or confidential financial or medical information has been revealed in violation of the law."
The need for a shield law began back in 1972 when reporter Paul Branzburg wrote about the drug hashish. After finding and questioning two locals who had created and used the drug, Branzburg promised to keep their names confidential. However, when the piece was printed, Branzburg was subpoenaed by a grand jury and asked to reveal his sources. Branzburg refused.
Eventually, the case came to the U.S. Supreme Court "where the court decided in a five to four decision that the press did not have a Constitutional right of protection from revealing confidential information in court. The court acknowledged, however, that the government must convincingly show a substantial relation between the information sought and a subject of overriding and compelling state interest," states en.wikipedia.org. "While this ruling did not set a precedent for journalistic rights in court, it did define a more stringent set of requirements for when a journalist could be subpoenaed in court."
