Five years after Congress authorized warrantless electronic spying, the Obama administration has never divulged to a single defendant that they were the target of this type of phone or e-mail surveillance—despite lawmakers’ claims the snooping has stopped terrorist plots and resulted in arrests.

The reason federal prosecutors are keeping mum, and perhaps violating federal rules requiring the government to tell defendants where evidence was obtained, is because such a concession would pave the way for a challenge to the constitutionality of the surveillance tactics, which Congress approved in 2008 and then again in December.

Against that backdrop, the American Civil Liberties Union filed a new lawsuit today in a New York federal court against the Justice Department, demanding an accounting of the defendants ensnared under the law, known as the FISA Amendments Act, which codified President George W. Bush’s once-secret spy program adopted in the wake of the September 11, 2001 terror attacks. The suit is in response to the government not answering the civil rights group’s Freedom of Information Act request in March.

The suit (PDF) said that the Justice Department’s failure to “release responsive records is of particular concern because the request relates to a highly controversial surveillance authority whose wisdom, effectiveness, and legality is a matter of intense and ongoing public debate.”

The suit comes as US Solicitor General Donald Verrilli Jr. reportedly is arguing internally that there is “no legal basis” for failing to disclose to defendants if they were a target of the warrantless surveillance. To be sure, there’s been plenty of defendants ensnared under the program.

In Senate hearings in December, just days before the legislation was set to expire. Sen. Dianne Feinstein (D-CA) successfully urged her fellow lawmakers to do what the House had done: Reauthorize the act for another five years. She described at least nine terror plots that were broken up by the program, and said “There have been 100 arrests to prevent something from happening in the United States, some of these plots have been thwarted because of this program. I think it is a vital program.” (PDF)

The government’s secrecy on the matter was pivotal in killing a challenge to the legislation before the Supreme Court.

In a 5-4 ruling in February, the justices set aside the ACLU’s challenge because the plaintiffs—journalists and human rights groups the ACLU was representing—had no evidence they were surveilled under the authority of the FISA Amendments Act.

But the court’s decision did not foreclose a constitutional challenge. The justices said that, if the government “intends to use” evidence obtained in such a manner, “the government must provide advance notice of its intent, and the affected person may challenge the lawfulness of the acquisition.”

The act generally requires the Foreign Intelligence Surveillance Court to rubber-stamp terror-related electronic surveillance requests. The government does not have 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 was adopted in the wake of the President Richard M. Nixon Watergate scandal, and provided authorities a way to conduct authorized surveillance in secret while under the auspices of a court for the purpose of acquiring “foreign intelligence.”

The government’s change of heart on whether disclosure was required first became public in the prosecution of brothers accused of plotting to blow up a high-profile target in New York City.

The terrorism case concerns brothers Raees Alam Qazi, 20, and Sheheryar Alam Qazi, 30.

Among other things, prosecutors said the younger Pakistani-born brother surfed al-Qaeda internet sites to learn how to build a bomb. The FBI recorded telephone calls allegedly linking him to a plot to blow up a New York landmark last year.

In May, the authorities said doing so would disclose “sensitive national security information.”

But in July, the authorities said it “does not intend to use any information obtained or derived from FAA-authorized surveillance.” The government did not say, however, whether it has such evidence or built a case on it.

But the authorities said that its May filing “is not the government’s position.”

This story originally appeared on Wired.