The National Assn. of Broadcasters is questioning the constitutionality of a record fine the FCC issued against a Roanoke, Va., TV station for airing a sexually explicit video clip of an adult film website during a news broadcast.

In March, the FCC announced its plans to issue to WDBJ-TV a fine of $325,000 — the highest ever levied against a TV station for a single incident of airing indecent content.

The NAB, in a filing with the FCC, said the fine “improperly intrudes into broadcasters editorial discretion.” The organization said the FCC “inexplicably exacerbated its constitutionally suspect regulatory approach by proposing the highest indecency fine ever against a single station, which had inadvertently aired a fleeting sexual image in a newscast. Levying the maximum possible fine under the law in a case where the broadcast station indisputably did not purposefully air the image at issue is tantamount to imposing a sentence of life imprisonment for petty theft.”

The NAB was joined in its filing by the Radio Television Digital News Assn.

The fine came in response to complaints over the station’s July 12, 2012, newscast that featured a report on a former adult film star who joined a local volunteer rescue squad.

The station argued that it did been aware of the indecent material when it broadcast the screenshot of the adult film website. The images were featured in a small box on the adult film site, which a station photojournalist said he did not notice before the report was broadcast during a 6 p.m. newscast.

Broadcasters’ challenge of FCC sanctions over so-called fleeting expletives and indecent content have twice gone to the Supreme Court. In 2012 the Supreme Court struck down fines against Fox and ABC over fleeting material, finding that the networks were not given a fair notice of a change in policy. It stopped short, however, of revisiting the broader question of regulation of indecent content on the airwaves.

Broadcasters argue that the FCC’s fine was issued even though the agency has taken no action to clarify its indecency policy. They also say that news broadcasts are entitled to a higher level of First Amendment protection.

The NAB said the FCC’s action imperils broadcast coverage of live events, as the agency’s rationale “threatens to turn almost every human error, equipment failure or unpredictable occurrence resulting in the airing of arguably indecent material into a deliberate, intentional violation of federal criminal law and FCC regulation.”

It also contends that the fine “appears to be based, in substantial part, on the FCC’s displeasure with WDBJ’s editorial judgment and choice of news content.”

An FCC spokeswoman had no comment.