News outlets around the United States are facing a political onslaught from allies of President Trump. A newspaper synonymous with Long Island is fighting back.

A legal filing this week by the publication, Newsday, signals that it will sue Nassau County for repeatedly violating its First Amendment rights. It accused the county and its powerful executive, Bruce Blakeman, of retaliating for its coverage of Mr. Blakeman’s administration, which has taken high-profile steps to demonstrate support for Mr. Trump’s most divisive policies.

The complaint to be filed in the Eastern District of New York accuses officials of ignoring Newsday’s reporters and illegally revoking its status as the official newspaper of Nassau County, thus removing an important revenue stream from paid public notices. That distinction was awarded to the conservative New York Post in December.

“The residents of Nassau County have the right to transparency from their government officials, and taxpayer dollars should never be used to intimidate the press and limit information the public needs,” Debby Krenek, Newsday’s publisher, said in a statement.

Chris Boyle, a spokesman for Mr. Blakeman, wrote in an emailed statement that the lawsuit was “foolish, frivolous and completely devoid of merit.”

“The Blakeman administration regularly communicates with all members of the media, including Newsday,” Mr. Boyle wrote.