Local lawmakers may have to release several hundred pages of additional documents about the redevelopment of the McMillan Sand Filtration site following a recent decision by the D.C. Court of Appeals.

A three-judge panel last week ruled that the D.C. Council cannot withhold certain documents relating to the controversial project in Northwest based on a “speech and debate” exemption applied to the District’s Freedom of Information Act. Opponents of the site’s redevelopment call the ruling a victory because of the transparency the documents—including emails between Wilson Building staff and developers—would provide. Still, the case has been remanded to D.C. Superior Court, meaning Council attorneys could seek to exempt records from disclosure through other statutes.

Kirby Vining, one of the cofounders of Friends of McMillan Park, had filed a FOIA request a couple years ago that was in part denied by the Council. But on June 9, the Appeals Court ruled that the Council hadn’t sufficiently argued that a law meant to protect its staff from being subject to some litigation covered the exemption it had sought. (It’s called the Legislative Privilege Act.)

“The force compelling the Council to disclose its records is none other than legislation drafted by the Council itself,” Associate Judge Catharine Easterly wrote in the decision, alluding to D.C.’s relatively expansive FOIA laws. “If the Council wants to minimize its obligations under D.C. FOIA, it can do so, either by amending D.C. FOIA or by amending the Legislative Privilege Act to make it clear that it specifically exempts from disclosure particular Council documents. In the meantime, this court must enforce the law currently on the books.”

Easterly explained that the statute the Council had evoked to avoid disclosing documents didn’t apply to Vining’s case because it only prohibits “question[ing] Councilmembers in ‘any other place’ regarding ‘any speech or debate made in the course of legislative duties.’” Had it applied, the Council could “withhold swaths of public documents in direct conflict with FOIA’s open-government mission,” the judge added.

Don Padou, Vining’s lawyer, says the court’s ruling sets precedent that the speech-and-debate clause cannot be interpreted broadly so as to prevent the Council from disclosing public records. But because the case has been remanded to a trial court, Wilson Building attorneys could attempt to invoke the “deliberative process” exemption, which protects staffers from having to censor their advice to representatives.

Padou says he expects that D.C. Superior Court will resolve the case “sometime this summer.”

“What is in those emails, we’ll find out,” he says. “How long it takes, we don’t know.”

You can read the court’s full ruling here.

Andrew Giambrone contributed reporting.