The FISA Amendments Act, (.pdf) which was expiring Friday at midnight, allows the government to electronically eavesdrop on Americans’ phone calls and e-mails without a probable-cause warrant so long as one of the parties to the communication is believed outside the United States. The communications may be intercepted “to acquire foreign intelligence information.”

The House approved the measure in September. President Barack Obama, who said the spy powers were a national security priority, is expected to quickly sign the package before the law Congress codified in 2008 expires in the coming hours. Over the past two days, the Senate debated and voted down a handful of amendments in what was seen as largely political theater to get Sen. Ron Wyden (D-Oregon) to lift a procedural hold on the FISA Amendments Act legislation that barred lawmakers from voting on the package.

In the end, the identical package the House passed 301-118 swept through the Senate on a 73-23 vote.

Amendments senators refused to enact included extending the measure for just three years, another one requiring the government to account for how many times Americans’ communications have been intercepted, and one by Wyden prohibiting U.S. spy agencies from reviewing the communications of Americans ensnared in the program.

“The amendment I fought to include would have helped bring the constitutional principles of security and liberty back into balance and intend to work with my colleagues to see that the liberties of individual Americans are maintained,” Wyden said immediately after the vote.

The legislation does not require the government to identify the target or facility to be monitored. It can begin surveillance a week before making the request, and the surveillance can continue during the appeals process if, in a rare case, the secret FISA court rejects the surveillance application. The court’s rulings are not public.

The government has also interpreted the law to mean that as long as the real target is al-Qaeda, the government can wiretap purely domestic e-mails and phone calls without getting a warrant from a judge. That’s according to David Kris, a former top anti-terrorism attorney at the Justice Department.

In short, Kris said the FISA Amendments Act gives the government nearly carte blanche spying powers.

Kris, who headed the Justice Department’s National Security Division between 2009 and 20011, writes in the revised 2012 edition of National Security Investigations and Prosecutions:

For example, an authorization targeting ‘al Qaeda’ — which is a non-U.S. person located abroad—could allow the government to wiretap any telephone that it believes will yield information from or about al Qaeda, either because the telephone is registered to a person whom the government believes is affiliated with al Qaeda, or because the government believes that the person communicates with others who are affiliated with al Qaeda, regardless of the location of the telephone.

The National Security Agency told lawmakers that it would be a violation of Americans’ privacy to disclose how the measure is being used in practice.

After Obama signs the legislation Friday, the spy powers won’t expire until December 31, 2017.

The law is the subject of a Supreme Court challenge. The Obama administration argues that the American Civil Liberties Union and a host of other groups suing don’t have the legal standing to even bring a challenge.

A federal judge agreed, ruling the ACLU, Amnesty International, Global Fund for Women, Global Rights, Human Rights Watch, International Criminal Defence Attorneys Association, The Nation magazine, PEN American Center, Service Employees International Union and other plaintiffs did not have standing to bring the case because they could not demonstrate that they were subject to the warrantless eavesdropping.

The groups appealed to the 2nd U.S. Circuit Court of Appeals, arguing that they often work with overseas dissidents who might be targets of the National Security Agency program. Instead of speaking with those people on the phone or through e-mails, the groups asserted that they have had to make expensive overseas trips in a bid to maintain attorney-client confidentiality. The plaintiffs, some of them journalists, also claim the 2008 legislation chills their speech, and violates their Fourth Amendment privacy rights.

Without ruling on the merits of the case, the appeals court agreed with the plaintiffs last year that they have ample reason to fear the surveillance program, and thus have legal standing to pursue their claim.

The case, argued last month, is pending an opinion from the Supreme Court.