wPolsce24 said on Thursday its lawyers had concluded that police had failed to provide a sufficiently clear legal basis to require the release of unpublished journalistic footage.
The station said it therefore refused to provide the recordings.
"We will certainly not hand over any recordings from outside the Constitutional Tribunal to this government," editor-in-chief Jacek Karnowski said, arguing that the material could be used to identify protest participants.
Karnowski described the visits by plainclothes officers as "extremely troubling and unprecedented in press practice," although he acknowledged that requests for journalistic material were sometimes made during criminal investigations.
Police also sought recordings and documents from TV Republika, another conservative broadcaster.
Plainclothes officers delivered the demand to the station's Warsaw headquarters on Thursday.
The requests concern an October 16 protest outside Poland's Constitutional Tribunal, which rules on whether legislation complies with the constitution.
Prosecutors in the northwestern city of Szczecin opened an investigation following a complaint by Interior Minister Marcin Kierwiński.
They are examining suspected offenses against police officers and the prime minister, including public insults, attempts to interfere with police duties and calls to disclose a female officer's private information.
Julia Szozda, spokeswoman for the District Prosecutor's Office in Szczecin, said the demands made to TV Republika did not include electronic equipment or material protected by journalistic confidentiality.
She said investigators were seeking the recordings and documents to establish the course of events and determine whether they had obtained all relevant material, including footage that had not been broadcast.
Prosecutors also requested broadcast-system logs, records used to produce on-screen news captions, staff schedules, duty assignments and licensing documents, state news agency PAP reported.
(rt/gs)
Source: PAP