WHEN CAN THE government snoop on you in the name of national security? The acrimonious war over that big question is reigniting.

The Supreme Court on Monday will hear part of a suit from the American Civil Liberties Union (ACLU) challenging the 2008 amendments to the Foreign Intelligence Surveillance Act (FISA). In addition to modernizing FISA, originally drafted in 1978, the ACLU and others claim the 2008 amendments weakened already loose limits on the government’s ability to spy on Americans. Among other things, they theorize that government agents can conduct “dragnet” data collection that could ensnare the electronic communications of thousands or even millions of U.S. citizens, as long as the spying isn’t targeted at U.S. citizens. There are not enough protections, they argue, of Americans’ Fourth Amendment freedom from unreasonable searches.

It’s hard even to discuss how the system operates because it’s secret. That means it’s also hard to challenge in court. The government argues that people can’t sue unless they can show they’ve been harmed. The plaintiffs say they suspect they may have been or will be caught up in surveillance, but that since the program is secret, by design and necessity, they might never know for sure. The best they can do is claim they have a reasonable suspicion that the government has or will come across their e-mails or phone calls. The court might well find that reasoning insufficient to sustain the ACLU’s suit, because the activists’ court challenge would proceed without the sort of specific, factual record that normally underlies constitutional disputes.

If the Supreme Court effectively insulates FISA from court challenge, the ACLU’s best chance for review would probably not be in court but in Congress. The FISA amendments are set to sunset later this year. The House has passed a reauthorization bill, but the Senate has not. The issue has not gotten much attention. But the advance of telecommunications technology and the role of that technology in Americans’ lives are important subjects that will be forced on lawmakers in their lame-duck session.

Discomfort with the government’s capacity, technical or legal, to collect and retain massive amounts of personal information is understandable. But the 2008 FISA amendments sought a compromise between two essential goals: preserving American liberty and robustly defending Americans’ lives and property. We favored the law and believe that it should be extended. A key plank of that balancing was enhanced congressional monitoring of executive-branch surveillance. Both in their review this year and going forward, lawmakers need not be — and should not be — toothless in their oversight.