Two documentary film-makers are facing decades in prison for recording US oil pipeline protests, with serious felony charges that first amendment advocates say are part of a growing number of attacks on freedom of the press.

The controversial prosecutions of Deia Schlosberg and Lindsey Grayzel are moving forward after a judge in North Dakota rejected “riot” charges filed against Democracy Now! host Amy Goodman for her high-profile reporting at the Dakota Access pipeline protests.

But authorities in other parts of North Dakota and in Washington state have continued to target other film-makers over their recent reporting on similar demonstrations, raising concerns that the lesser-known journalists are not getting the same kind of public support and national attention.

Schlosberg, a New York-based film-maker, is facing three felony conspiracy charges for filming protesters on 11 October at a TransCanada Keystone Pipeline site in Pembina County in North Dakota, with prosecutors alleging that she was “recruited to record the criminal activity”.

The 36-year-old – who produced a documentary called How to Let Go of the World and Love All the Things Climate Can’t Change – could face 45 years in prison. US whistleblower Edward Snowden recently tweeted his support of Schlosberg, writing: “This reporter is being prosecuted for covering the North Dakota oil protests. For reference, I face a mere 30 years.”

This reporter is being prosecuted for covering the North Dakota oil protests. For reference, I face a mere 30 years. https://t.co/GzMbwCVV40 — Edward Snowden (@Snowden) October 14, 2016

Grayzel, an independent film-maker from Portland, Oregon, was also arrested and jailed on 11 October while filming at a separate pipeline protest in Skagit County, Washington. She and her cinematographer, Carl Davis, had their footage and equipment seized and were kept behind bars for a day.

The two were filming activist Ken Ward attempting to shut down the Trans Mountain pipeline, and they now face 30 years in prison for a felony burglary charge, a felony “criminal sabotage” charge and a misdemeanor trespass offense. There were a series of pipeline protests across the US on 11 October.

“Everyone needs to be afraid when our first amendment rights are in jeopardy,” Grayzel, 41, told the Guardian on Thursday before her criminal arraignment. “This is not just about me. This is not just about Carl. This is not about Amy Goodman … This is about the public’s right to know what is going on in this country.”

Free-speech advocates said that both cases are unusual and troubling given that prosecutors have admitted that the defendants were acting as film-makers and are still pursuing aggressive felony cases.

Lindsey Grayzel: ‘Everyone needs to be afraid when our first amendment rights are in jeopardy.’ Photograph: Ben Grayzel

While it’s not uncommon for journalists to face arrest and misdemeanor charges for trespassing or disorderly conduct while reporting at controversial protests, conspiracy, burglary and sabotage offenses are rare for members of the media.

“It’s outrageous. It’s an assault on the first amendment,” said Neil Fox, one of Grayzel’s attorneys. “It’s shocking, but it is the kind of climate that we’re living in right now.”

Fox cast blame on the Republican presidential candidate, Donald Trump, who has made vicious attacks on the media a cornerstone of his campaign. “This is certainly the result of the toxic language that Trump brings to the election.”

Although Ward, a climate activist, had gained access to a fenced enclosure owned by the Trans Mountain Pipeline, the Skagit County sheriff’s report noted that Grayzel and her cinematographer were “just outside the enclosure … taking photographs and video”. The report said they confiscated the film-makers’ phone and “assorted camera equipment”, actions that have raised further concerns about press intimidation and free speech violations.

Washington prosecutors are relying on laws that were passed in the early 20th century to target labor rights’ protesters, Fox added. “There’s been a revival in the state of Washington of the use of these statutes against labor activists and against environmental activists.”

In Goodman’s case, a judge forced prosecutors to drop a serious “riot” charge, which was centered on Goodman’s viral coverage of the intense Native American-led protests. But prosecutors and sheriff’s officials said they may continue to pursue other charges against the critically acclaimed journalist.

In Schlosberg’s charges, North Dakota prosecutors have alleged that she was part of a conspiracy, claiming she traveled with protesters “with the objective of diverting the flow of oil”.

“I was surprised at the conspiracy charges. I never thought that would ever happen,” her attorney Robert Woods told the Guardian. “All she was doing was her job of being a journalist and covering the story.”

Prosecutors in both cases declined to comment.