Sheen's admittedly raucous lifestyle, substance abuse, stints in rehab and fondness for dating porn stars have overshadowed for years the career of the former TV star of "Two and a Half Men."
The latest commotion has crossed from celebrity gossip to a battle over press freedom and a possible criminal case.
Los Angeles police have opened a criminal investigation of Sheen, and on Tuesday served a search warrant on the New York headquarters of American Media Inc, the parent company of both RadarOnline and the Enquirer.
Sheen's attorney and agent did not respond to requests for comment.
Dylan Howard, editor-in-chief of the Enquirer and editorial director of RadarOnline, told Reuters the two outlets had no plans to turn over documents or identify their sources.
He said the search warrant, signed by a Los Angeles County Superior Court judge, was illegal under both state and federal law that prevents the use of such warrants against media organizations relating to "newsworthy" information.
"We do believe that a judge did issue this order against the law, and that's why we will not be complying with its order," Howard said in an interview. The LAPD should emulate the two publications and "uncover the evidence" themselves, he added.
There were conflicting views on the legality of warrant.
Terry Francke, general counsel for Californians Aware, a non-profit journalists' rights advocacy group, said the Los Angeles Police Department warrant was "flatly illegal" under California law.
Jonathan Kotler, journalism professor at the University of Southern California, said there has been little clarity on the issue. The courts "have been all over the place through the years" on so-called shield laws protecting journalists, he said.
"Courts don’t like shield laws much," Kotler added.
The two publications first reported on the audio in late March, saying it was recorded by an unnamed former lover of Sheen. They have reported quotes but have not made the audio available online. Reuters could not verify the voice is Sheen's.
According to a copy of the search warrant and an affidavit provided on Thursday by RadarOnline, the Los Angeles police investigation was triggered by Scottine Ross, a former porn actress and onetime fiancee of Sheen, who accused Sheen in a December lawsuit of assault and of having sex with her without revealing he was HIV positive.
The affidavit says Ross went to police fearing for her life on March 31 after reading the RadarOnline and Enquirer accounts of threatening statements Sheen allegedly made about her in calls to another unidentified woman.
Sheen announced in a November interview that he had been diagnosed with HIV about four years earlier, but said it was "impossible" that he had transmitted the virus to anyone else.