When can the government snoop on you in the name of national security? The acrimonious war over that question is reigniting.

The Supreme Court on Monday heard part of a suit from the American Civil Liberties Union challenging the 2008 amendments to the Foreign Intelligence Surveillance Act. In addition to modernizing FISA, 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 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 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. If the Supreme Court effectively insulates FISA from court challenge, the ACLU’s best chance 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 advance of telecommunications technology and its role in Americans’ lives are important subjects that will be forced on lawmakers in their lame-duck session.

Discomfort with the government’s capacity to collect and retain massive amounts of personal information is understandable. But the 2008 FISA amendments sought a compromise between preserving American liberty and robustly defending Americans’ lives and property. 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.