A US congressman has introduced a bill that could send anti-fascist activists to prison for up to 15 years for protesting in masks.

The bill, introduced by Republican Representative Dan Donovan, imposes penalties on anyone who “injures, oppresses, threatens, or intimidates” another person while wearing a mask or disguise.

While the text of the bill itself does not mention anti-fascist activists, the name is more explicit: “The Unmasking Antifa Act of 2018.”

“Antifa” is shorthand for a loosely organised group of left-wing protesters who track and protest neo-Nazi organising in their areas. Occasionally, the activists dress in black and cover their faces to conceal their identities.

Passing a bill to criminalise these tactics, some antifa activists said, could jeopardise their safety and embolden right-wing protesters.

“This bill explicitly targets the tactics used by anti-fascists to protect themselves against the violence and harassment of the far-right groups who routinely target them,” said Janine Renee Cunningham, a member of New York’s Metropolitan Anarchist Coordinating Council, in a statement to The Independent.

She added: “As a result, it should be considered tacit support of not only fascism, but also dangerous alt-right groups in this country.”

White supremacists clash with anti-fascist campaigners ahead of Virginia rally

Anti-fascist organising gained notoriety last year, after activists showed up to counter-protest a white supremacist rally in Charlottesville, Virginia. One counter-protester, 32-year-old Heather Heyer, was killed by an attendee at the event, who acquaintances have identified as a Nazi sympathiser.

President Donald Trump condemned Ms Heyer’s death at the time, but also blamed violence at the rally on “both sides”. He later singled out the “far left” for criticism, accusing them of violently charging at the rally attendees.

Walter Shaub – the former head of the US Office of Government Ethics, who resigned in protest under Mr Trump – tweeted about Mr Donovan's bill on Tuesday.

“Two groups go to Charlottesville. A big group chants racist filth, wields semi-automatic assault rifles, fires a gun into a crowd & murders a woman with a car. A small group wears masks," he wrote. "It’s the small group these Congressmen want to lock up for 15 years. Authoritarianism rises.”

Violence on the streets of Charlottesville Show all 9 1 /9 Violence on the streets of Charlottesville Violence on the streets of Charlottesville Protesters clash and several are injured White nationalist demonstrators clash with counter demonstrators at the entrance to Lee Park in Charlottesville, Virginia. A state of emergency is declared, August 12 2017 Violence on the streets of Charlottesville Trump supporters at the protest A white nationalist demonstrator walks into Lee Park in Charlottesville, Va., Saturday, Aug. 12, 2017. Hundreds of people chanted, threw punches, hurled water bottles and unleashed chemical sprays on each other Saturday after violence erupted at a white nationalist rally in Virginia. AP Photo Violence on the streets of Charlottesville State police stand ready in riot gear Virginia State Police cordon off an area around the site where a car ran into a group of protesters after a white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville Militia armed with assault rifles White nationalists, neo-Nazis and members of the 'alt-right' with body armor and combat weapons evacuate comrades who were pepper sprayed after the 'Unite the Right' rally was declared a unlawful gathering by Virginia State Police. Militia members marched through the city earlier in the day, armed with assault rifles. Getty Images Violence on the streets of Charlottesville Statue of Confederate General Robert E Lee The statue of Confederate General Robert E. Lee stands behind a crowd of hundreds of white nationalists, neo-Nazis and members of the 'alt-right' during the 'Unite the Right' rally 12 August 2017 in Charlottesville, Virginia. They are protesting the removal of the statue from Emancipation Park in the city. Getty Images Violence on the streets of Charlottesville Racial tensions sparked the violence White nationalists, neo-Nazis and members of the 'alt-right' exchange insults with counter-protesters as they attempt to guard the entrance to Lee Park during the 'Unite the Right' rally Getty Violence on the streets of Charlottesville A car plows through protesters A vehicle drives into a group of protesters demonstrating against a white nationalist rally in Charlottesville, Virginia. The incident resulted in multiple injuries, some life-threatening, and one death. AP Photo Violence on the streets of Charlottesville Rescue personnel help injured people after a car ran into a large group of protesters after an white nationalist rally in Charlottesville, Virginia AP Photo Violence on the streets of Charlottesville President Donald Trump speaks about the ongoing situation in Charlottesville, Virginia from his golf club in Bedminster, New Jersey. He spoke about "loyalty" and "healing wounds" left by decades of racism.

Ryan Patrick, a spokesperson for Mr Donovan, told The Independent that the bill was not intended to target any one group in particular. He noted that the bill simply would simply update existing civil rights statutes to add a penalties for wearing a mask.

But a fact sheet sent out by his Mr Donovan's office highlighted alleged acts of violent violence by antifa activists – including a rally in Berkeley, California, where protesters threw Molotov cocktails before an appearance by right-wing provocateur Milo Yiannopoulos.

“Americans have the natural right to speak and protest freely; it is not a right to throw Molotov cocktails and beat people while hiding behind a mask,” Mr Donovan, who represents New York, said of the bill in a statement.

Domestic extremists of all kinds killed at least 372 people in the US between 2007 and 2016, according to the Anti-Defamation League. Of those deaths, approximately 74 per cent were at the hands of right-wing extremists. Two per cent were carried out by left-wing extremists.

Michael Loadenthal, a professor of sociology and social justice at Miami University, said he did not think Mr Donovan's bill was designed to protect Americans from violence, but instead to discourage protest.

“Even if this bill never gets passed ... it’s designed to show people that there could be very severe consequences for what is seen as a self-defensive manoeuvre,” he said, referring to the tactic of wearing a mask.