A debate over how freely the U.S. government can eavesdrop on international communications reaches a climax on Monday in the country’s highest court.

At issue is a law passed by Congress in 2008 allowing the government to monitor the overseas communications of individuals without obtaining a warrant for each target.

The government has said it needs flexible surveillance power to help prevent strikes by foreign militants such as the attacks of Sept. 11, 2001.

But a group of attorneys, journalists and human rights organizations has challenged the law, saying thousands or even millions of innocent Americans are likely being monitored merely because they are communicating with people overseas.

In oral arguments on Monday, the U.S. Supreme Court will consider whether the challengers have the right to bring a suit against the law.

The government argues that, because the surveillance is secret, the challengers cannot prove they have been harmed by the law and therefore do not have standing to challenge it.

The challengers argue that they are harmed because they must travel to meet their clients and sources in person, to avoid wiretaps. Human Rights Watch, one of the challengers, has had to pay for more plane tickets, translators, drivers and guides because of the law, the group’s general counsel, Dinah PoKempner, said.

Although the question of standing is a technical one, a victory for the government could end the challenge to the law.

If the government prevails at this stage, it will have shielded its surveillance laws from review by the courts, said Jameel Jaffer, a lawyer who represents the individuals and organizations challenging the law.

It’s unclear how the high court will rule. Since the Sept. 11 attacks, the court has shown a reluctance to intervene in the executive branch’s national security and intelligence-gathering procedures. The fact that the court took the case means that at least four justices saw problems with a lower court ruling allowing the case to proceed.

Congress passed the original Foreign Intelligence Surveillance Act in 1978 to clamp down on government spying, which had escalated in the 1960s and 1970s. The law required the government to submit a surveillance application to a special court for each overseas individual it was targeting.

After the attacks of Sept. 11, 2001, President George W. Bush authorized the National Security Agency’s use of warrantless wiretaps in the hunt for people with ties to al Qaeda and other militant groups. The Bush administration ended that program in 2007, but Congress legalized parts of it in an overhaul of the Foreign Intelligence Surveillance Act in 2008.

Under the new law, the government no longer has to provide the court with specific names, phone numbers or email addresses of people to be tapped. Instead, it can apply for permission to conduct mass surveillance merely by stating that it plans to monitor non-U.S. persons overseas to gather foreign intelligence.

The challengers filed a lawsuit saying the new procedures violate the U.S. Constitution’s Fourth Amendment protection against unreasonable search and seizures by allowing the government to sweep up communications with little judicial oversight.

One of the challengers, David Nevin, who is a lawyer for the accused Sept. 11 mastermind Khalid Sheikh Mohammed, said the 2008 law puts lawyers on the “horns of a dilemma.”

Ethics rules prohibit lawyers from holding sensitive conversations with clients when there’s a chance the government is eavesdropping, he said. As a result, Nevin limits what he says by phone and email and instead travels to Guantanamo Bay, Cuba, to talk to his client. But those constraints can make it harder to provide the effective legal assistance that ethical rules also require.

“We’ve gone back to the Stone Age,” said Tina Foster, a human rights lawyer who joined a brief in support of the challengers. “It’s like eliminating the benefit of telecommunication and access to information.”

In 2009 a federal district court in New York found that the challengers failed to prove they had been harmed by the law. But in 2011 the 2nd U.S. Circuit Court of Appeals disagreed, allowing the suit to proceed based on the plaintiffs’ fear of surveillance and the cost of trying to avoid it.

The government then petitioned the Supreme Court, arguing that the challengers did not have standing to bring their suit. To have standing, the challengers had to show that their injuries were “actual or imminent, not conjectural or hypothetical,” the government said in its petition.

Six former U.S. attorneys general have submitted a brief supporting the government, warning that allowing the suit to proceed would open the floodgates to litigation that would risk exposing state secrets.

The Justice Department declined to comment before Monday’s oral arguments.

In separate litigation, civil liberties groups tried to hold phone companies including AT&T Inc, Sprint Nextel Corp and Verizon Communications Inc accountable for helping the government eavesdrop on private conversations. A federal appeals court in December found the companies immune to the suits, and the Supreme Court this month declined to review that case.

(Reuters)