Out of nine high-profile cases since 2003 where journalists were ordered to reveal information, four might have turned out differently had the proposal awaiting Senate action been law.
For them and dozens of other reporters subpoenaed for confidential information or the names of those providing that information, judges generally would have to weigh the "public interest" of the media reports; that is a factor many judges already consider. They would retain the power to jail reporters who refuse to name sources who leak information involving national security.
If the Senate bill were law, former New York Times reporter Judith Miller still may have gone to jail for 85 days for refusing to identify the government official who breached national security rules by leaking a CIA agent's name.
But two San Francisco reporters might not have faced the prospect of 18-month jail terms for refusing to name the source for leaks of secret grand jury testimony that shed light on a steroid scandal in professional baseball.
Former USA Today reporter Toni Locy might benefit if a judge assigns enough "public interest" value to her reports about the government's investigation into the 2001 anthrax attacks. For now, she faces fines of up to $5,000 a day unless she discloses her Justice Department sources. This ruling, if embraced by other courts, could confront reporters with the prospect of bankruptcy for protecting sources.
Supporters of the Senate bill and a House-passed version cite press reports about secret CIA prisons, warrantless wiretaps of U.S. citizens and top Nixon administration officials' crimes that came to light through confidential sources.
"Reporters, editors, publishers and their lawyers cannot with assurance articulate the rules governing confidentiality because legal standards are hopelessly muddled," said Ted Olson, a former solicitor general in the Bush administration who is backing a shield law to create uniformity in the courts.
"Fearing the consequences of exposure, sources withdraw," Olson said.
The administration opposes both versions and says it would be nearly impossible to enforce laws against unauthorized releases of classified information.
The government would have to provide evidence of "significant and articulable harm" to national security - rather than a general claim - in addition to making judges weigh the public interest in protecting confidential sources.
Attorney General Michael Mukasey has said the Senate bill defines a journalist too broadly.
News organizations win about 60 percent of state and federal cases involving reporters' privilege each year, with journalists losing more often when a grand jury is involved, according to a 2007 analysis by media lawyer James Goodale.
Goodale, who represented The New York Times as its general counsel in the Pentagon Papers case, is the architect of the news media's largely successful legal strategy since a 5-4 Supreme Court decision in 1972 against reporters ordered to testify before a grand jury.
But the fifth vote in that case, by Justice Lewis Powell, left the door open for state and lower courts to allow a reporters' privilege by considering First Amendment interests of publicizing information.
Since then, 33 states have passed shield laws and 16 others have established judicial precedents protecting reporters to some degree in state courts. Only Wyoming offers no protections for journalists.
Federal judges began offering leeway to reporters as well in civil litigation and criminal trials, so long as the information sought was not critical to the government's or plaintiff's case and was available elsewhere. At times, they protected journalists from having to disclose unpublished, nonconfidential material.
"By a stroke of genius, media attorneys were able to turn what was actually a loss for the press in 1972 into a qualified privilege for 30-plus years," said University of Arizona law professor RonNell Andersen Jones. "There is now an unsettled feeling among members of the press about whether this carefully constructed house of cards is going to be blown down."
Jones has come up with figures in a soon-to-be-released survey that indicate a rise in federal subpoenas following highly publicized media losses in recent years. Those defeats, she says, have emboldened more lawyers to subpoena journalists.
Her survey, which got responses from 761 news organizations, found 21 federal subpoenas seeking names of confidential sources in 2006 and an additional 13 seeking material other than a source's name that was received on condition of anonymity.
Those numbers are substantially higher than the 19 subpoenas since 1992 cited by the Justice Department when arguing that a federal shield bill is unnecessary. That count includes only subpoenas by department prosecutors who want reporters to disclose sources' identities to grand juries. The tally does not include civil lawsuits, cases involving special prosecutors or trial subpoenas by federal prosecutors seeking confirmation of material already published in news stories.
Some experts say the tipping point prompting some courts to rethink their prior inclinations to favor reporters was a ruling in 2003 by Richard Posner, a federal appeals court judge in Chicago. Posner said judges were wrong to give more leeway when a case did not involve grand juries and when reporters were seeking to protect nonconfidential material.
"Subpoenas should be reserved for the very rare case," said Patrick Fitzgerald, the special prosecutor who compelled scores of reporters to testify in the CIA leak case. "But there is national security information going out the door on a pretty staggering basis. You can't say there's not a lot of serious information being compromised."
Fitzgerald, a federal prosecutor who subpoenaed the telephone records of Times reporters Miller and Philip Shenon in a separate case, argues that a shield law is unneeded and potentially dangerous. He says federal prosecutors already are already bound by Justice Department guidelines to issue subpoenas only in compelling situations.
Dismissing notions that media subpoenas would dampen investigative reporting, Fitzgerald said, "Journalists have been saying the sky is falling since 1972 ... and that suddenly the stories will dry up. But I'm not seeing big blank spaces on the front page."
Media groups are not so sure.
They cite Locy's case in which she is refusing to identify a dozen Justice Department sources to lawyers for Steven Hatfill. The former Army scientist is suing the government for invasion of privacy after he came under scrutiny in the anthrax attacks. Locy says she cannot remember if her dozen sources specifically talked about Hatfill.
"If journalists can't find protection in the courts, then legislation is the only answer," said Nathan Siegel, a lawyer who represents the AP and other news organizations.
The shield legislation is supported by several media organizations, including the AP, the Newspaper Association of America, the American Society of Newspaper Editors, The New York Times Co. and The Washington Post.