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Last month, Sen. Mark Udall and a handful of other privacy-focused politicians persuaded the IRS to promise to cease warrantless searches of Americans' private correspondence.

Now Udall, a Colorado Democrat, is taking aim at the Justice Department, which has claimed the right to conduct warrantless searches of Americans' e-mail, Facebook chats, and other private communications.

"I am extremely concerned that the Justice Department and FBI are justifying warrantless searches of Americans' electronic communications based on a loophole in an outdated law that the U.S. Court of Appeals for the 6th Circuit ruled was unconstitutional," Udall said in a statement sent to CNET Thursday.

Udall's statement cites a CNET article yesterday that was the first to disclose the Justice Department and the FBI's electronic search policies. The article was based on internal government documents obtained by the American Civil Liberties Union.

The senator's statement urges Congress to move quickly to update the 1986 Electronic Communications Privacy Act -- enacted during an era of dialup modems and the black and white Macintosh Plus -- that currently does not require search warrants for all e-mail messages. The 6th Circuit ruled in 2010, however, that the privacy protections enshrined in the Fourth Amendment require police to obtain search warrants signed by a judge first.

Neither the Justice Department nor FBI immediately responded to a request for comment from CNET.

Nate Wessler, an ACLU staff attorney, told CNET that a legal fix is long overdue. "Senator Udall is absolutely right that Congress must update ECPA to protect the privacy of Americans' emails, text messages, and other electronic communications," he said Thursday.

The documents show that the U.S. Attorney for Manhattan circulated internal instructions saying a subpoena -- a piece of paper signed by a prosecutor, not a judge -- was sufficient to obtain nearly "all records from an ISP" including older e-mail messages. And the U.S. Attorney in Houston recently obtained "contents of stored communications" from an unnamed Internet service provider without asking a judge for a search warrant first.

After the IRS's warrantless e-mail access policy came to light last month, a dozen Republican and Democratic senators rebuked the agency. The senators' letter (PDF) opposing warrantless searches was signed by Udall, Mike Lee, R-Utah, Rand Paul, R-Ky., and Ron Wyden, D-Ore., and said: "We believe these actions are a clear violation of the Fourth Amendment's prohibition against unreasonable searches and seizures."

Steven Miller, the IRS' acting commissioner, eventually said during a Senate hearing that the policy would be changed.

After the 6th Circuit Court of Appeals' 2010 ruling in U.S. v. Warshak, a few e-mail providers, including Google, Microsoft, Yahoo, and Facebook, but not all, have taken the position that the Fourth Amendment mandates warrants for e-mail all over the country. The Justice Department, industry representatives say, has informally moved toward recognizing Warshak all over the country, but only for e-mail and not other stored data, such as Facebook chats, Twitter direct messages, Google Drive and Dropbox files, and so on.

Before the Warshak decision, the general rule since 1986 had been that police could obtain Americans' e-mail messages that were more than 180 days old with an administrative subpoena or what's known as a 2703(d) order, both of which lack a warrant's probable cause requirement and are less privacy protective.

A phalanx of companies, including Amazon, Apple, AT&T, eBay, Google, Intel, Microsoft, and Twitter, as well as liberal, conservative, and libertarian advocacy groups, have asked Congress to update ECPA to make it clear that law enforcement needs warrants to access private communications and the locations of mobile devices. Bills have been introduced in the House of Representatives and the Senate, and last month the Senate Judiciary committee approved one version of the legislation.