NY1's lawsuit against the mayor over his emails with an outside adviser is moving ahead. In court papers filed Wednesday, lawyers for the station and its co-plaintiff, the New York Post, argue that the city has failed to prove that the mayor's emails should be kept from the public. NY1's Grace Rauh filed the following report.

NY1's lawyers are taking aim at Mayor Bill de Blasio over his argument that emails he exchanges with the so-called "Agents of the City" should be protected from public disclosure. 

The station, along with the New York Post, sued over the issue in September. And on Thanksgiving Eve, the city responded, releasing 1,500 pages of emails between the outside adviser at the center of the case, Jonathan Rosen, and the mayor and other top city officials.

Rosen runs the communications firm BerlinRosen and represents major clients, like real estate developers and unions, who have business before City Hall. 

On Monday, the mayor told NY1 that he is de-deputizing his agents and that in the future, any emails they exchange with him will be made public by request. 

"It's obviously become a distraction," de Blasio said.

Court papers filed Wednesday state that the mayor's announcement "makes a mockery of Respondents' contention that private advisors like Mr. Rosen can only be effective if their communications with City Hall are protected by a cocoon of secrecy."

The media companies' lawyers also argue that the email release triggered by the lawsuit undercuts the city's case because the documents show Rosen is not an agent of the city, as the mayor has maintained. 

"Mr. Rosen is a free agent, representing paying clients while at the same time attending City Hall policy meetings and corresponding about matters of interest to both his clients and the Mayor."

In a statement, the mayor's press secretary said, "We will review the filing but haven't yet had the opportunity to since NY1 chose to bury the news at dusk in the 11th hour of the news cycle.”

To be clear, our filing is 19 pages long, a far cry from the 1,500 pages of emails the city released on Thanksgiving Eve.