Overzealous prosecutors are threatening the First Amendment by jailing journalists who are doing their jobs.

In a particularly egregious case, Jim Taricani, a Rhode Island TV reporter, was convicted last week of contempt of court because he refused to reveal the source who gave him a videotape of an FBI sting of government officials.

Taricani didn’t break the law by broadcasting the tape, and it didn’t affect the trial of a mayor’s aide shown taking a bribe. Both the aide and the mayor were convicted.

Nonetheless, Taricani faces a six-month jail sentence.

Reporters from Time magazine and the New York Times have also been held in contempt for refusing to reveal sources in an investigation about the disclosure of a CIA operative’s name by syndicated columnist Robert Novak.

In each case, the government is trying to turn independent journalists into federal agents. The efforts are an affront to the First Amendment and could create a chilling effect among working journalists, concerned that their investigations could lead to jail time.

Sen. Christopher Dodd of Connecticut has introduced federal legislation that would create a national shield law to protect journalists from hyperactive prosecutors and judges who place their own prerogatives above the protections of the U.S. Constitution. Already, 31 states and the District of Columbia have shield laws. Unfortunately, Maine does not have a shield law. It’s time to federalize the protections with national standards.

Dodd’s bill would not allow reporters to be forced to turn over their notes or photographic negatives or to reveal sources, with a few limited exceptions. A court could compel disclosure if there is an overriding public interest in the information or it could not be obtained elsewhere.

“Democracy is premised on an informed citizenry,” Dodd said during a D.C. press conference, covered by the Associated Press. “A free press is the best guarantee of a knowledgeable citizenry.”

Taricani’s case should make that obvious. A free, democratic society should not be in the business of jailing journalists. It’s time for a national shield law.