Bradley Moss of the Law Office of Mark S. Zaid in Washington, D.C., said Trump's explicit authorization for the memo's release, and the fact that it's based on DOJ material, could amount to "official acknowledgement" of the records some of his clients are suing for, including the FISA application and a summary of the dossier.

That would mitigate federal agencies' refusal to confirm or deny the existence of certain records. Moss said the situation presents a unique legal wrinkle when it comes to FOIA cases.

"There's no real precedent here," Moss said. "This is going to be uncharted waters."

Under FOIA case law, the government can be compelled to release information that has already been officially disclosed by the executive branch. Courts have not recognized congressional reports or statements as "official disclosure" under FOIA law.

Trump's signature could create an exception to that rule, Moss said. 

"This kind of blurs the lines a bit," Moss said. "We don't really know how the court will view it."

Moss said he has two pending cases that may be influenced by the memo's release. One, on behalf of USA Today reporter Brad Heath and the James Madison Project, seeks a copy of any application to the FISA court to collect information related to the Trump Organization, Trump's campaign or people associated with Trump, and any order approving that application. The case is pending in the federal district court in Washington, D.C.

Another, filed on behalf of Politico reporter Josh Gerstein and the James Madison Project, seeks the disclosure of a two-page synopsis outlining the contents of the dossier, as well as any determination by federal agencies as to its validity and records of efforts to investigate it. U.S. District Judge Amit Mehta of the District of Columbia granted summary judgment on behalf of the government in that case Jan. 4, and it's now on appeal before the D.C. Circuit.