shield law

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A law that limits the ability of a court to compel a journalist to give testimony disclosing sources of information.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun US, law legislation designed to provide a news reporter with the right to refuse to testify as to information and/or sources of information obtained during the news gathering and dissemination process.