Federal prosecutors filed the notice to the defendant in the Portland case, Mohamed Mohamud, late Monday. It was the second time that the Justice Department had made such a disclosure, after a similar move last month in a Colorado case that had not gone to trial. Mr. Mohamud was convicted of trying to use a weapon of mass destruction at a Christmas tree-lighting ceremony in 2010.

Image Mohamed Mohamud was convicted of trying to use a weapon of mass destruction at a Christmas tree-lighting ceremony in Portland, Ore., in 2010. Credit... Multnomah County Sheriff's Office, via Associated Press

The notices could lead to a Supreme Court test of whether such eavesdropping, approved by Congress in the 2008 FISA Amendments Act, is constitutional. The Supreme Court rejected a challenge this year by Amnesty International on the grounds that the plaintiffs could not prove that their communications had been intercepted under the law.

The Justice Department had urged the Supreme Court to reject that case. It said the law would still be subject to judicial review, because criminal defendants facing evidence derived from warrantless surveillance would be notified of that fact and have standing to challenge it.

But it has since emerged that it was not the practice of National Security Division prosecutors to tell defendants when warrantless wiretapping had led to evidence in a case, something Mr. Verrilli had not known at the time of the Supreme Court case, even though his briefs and arguments assuring the justices otherwise had been vetted by the division. After the discrepancy came to light, Mr. Verrilli fought an internal battle to bring department policy in line with what he had told the court, ultimately prevailing.

But the senators — Ron Wyden of Oregon, Mark Udall of Colorado and Martin Heinrich of New Mexico — raised a new issue in their letter: A government brief, a statement by Mr. Verrilli during oral arguments and a line in the majority’s ruling appeared to rely on the premise that Americans had to be in direct contact with someone abroad who had been targeted for surveillance for the N.S.A. to collect their communications without a warrant.