When the federal government wants some information under Section 215 of the Patriot Act—which allows agents to access “tangible things” like business records—it goes to the Foreign Intelligence Surveillance Court. This much we know.

What we don’t know is how broadly FISA interprets Section 215—what information it allows federal agents to access, and to what extent the government must prove “relevance” to a terrorism investigation.

Two men who do know, however—Senators Mark Udall and Ron Wyden of the Senate Intelligence Committee—have consistently sounded alarms about what FISA is allowing under Section 215. While unable to reveal specifically what they have learned, the two Senators have repeatedly said that the public would be shocked if it knew what information was being collected with the help of FISA and the Patriot Act.

This week, Udall and Wyden wrote to Attorney General Eric Holder asking him to address this issue (emphasis is theirs):

We believe most Americans would be stunned to learn the details of how these secret court opinions have interpreted section 215 of the Patriot Act. As we see it, there is now a significant gap between what most Americans think the law allows and what the government secretly claims the law allows. This is a problem, because it is impossible to have an informed public debate about what the law should say when the public doesn’t know what its government thinks the law says.

The two senators were spurred to write after learning the Justice Department wants to dismiss lawsuits filed by the American Civil Liberties Union and the New York Times that seek to find out exactly how the government is interpreting Section 215.

But it’s not the first time they’ve raised the issue, to Holder nor publicly—we’ve flagged it before here, and Wyden gave a dramatic speech on the Senate floor about this last year:

In 2009, the administration promised it would establish a process for “reviewing, redacting and releasing significant opinions” of FISA, but as the letter from Udall and Wyden notes, this hasn’t happened once.

One has to assume Udall and Wyden are legitimately disturbed by what they know—it’s extremely unusual for two senators to go so public about secret information they are privy to, and especially to prod a president (and former Senate colleague) from their own party. Will we ever know what has alarmed them?