A closely-watched civil trial that pits vote machine maker Dominion against Fox News and tests the extent of free speech rights for media in America -- even when broadcasting alleged election falsehoods -- is due to start Thursday with jury selection.

The proceedings could be one of the most consequential defamation cases ever heard in the United States and threaten financial and reputational damage for Rupert Murdoch's conservative TV network.

The stakes "are pretty high for Fox News," Nicole Hemmer, a historian specializing in media at Vanderbilt University in Nashville, Tennessee, told AFP.

Dominion Voting Systems sued Fox News in a Delaware court in March 2021 for $1.6 billion.

It alleges that the 24-hour news behemoth promoted Donald Trump's false claims that its machines were used to rig the 2020 presidential election that he lost to Joe Biden.

The company argues that Fox News aired the falsehoods while knowing they were untrue.

Dominion says that the network began endorsing Trump's conspiracy narrative because the channel was losing its audience after it became the first television outlet to call Arizona for Biden, projecting the Democrat would win the presidency.

Fox News denies committing defamation. It claims it was only reporting on Trump's allegations, not supporting them, and is protected by free speech rights enshrined in the First Amendment of the US Constitution.

A judge last month denied a bid by the right-leaning network to have the suit dismissed and ordered the case to go to trial.

"If found responsible for defamation, the network will potentially face a judgment in the neighborhood of $1 billion -- not enough to bankrupt the network, but enough to have real ramifications for its future planning and overall financial health," said Hemmer.

But that is a big if, as it is difficult for plaintiffs to win defamation suits in the United States due to the First Amendment.

'Actual malice'

Dominion will have to prove that Fox News acted with actual malice, a tough burden to meet.

That bar has been a bedrock of US media law since the 1964 New York Times Co. v. Sullivan case that saw the Supreme Court rule in the newspaper's favor.

Dominion's lawsuit has already proved embarrassing to Fox, however.

The 92-year-old Murdoch admitted in a deposition in the case that some on-air hosts had "endorsed" the false claim that the 2020 election was stolen from Trump.

He denied though that the network in its entirety had pushed the baseless claim, according to court documents filed by Dominion in February.

A separate filing showed that Murdoch had described comments by former Trump advisors Rudy Giuliani and Sidney Powell pushing Trump's claims as "really crazy stuff. And damaging."

Dominion's lawyers have also released a trove of internal Fox News communications that show what commentators really felt about Trump, who counted on Fox for steady support.

"I hate him passionately," star anchor Tucker Carlson said of the ex-president, despite being supportive on air.

Fox News has accused Dominion of "cherry-picking and taking quotes out of context."

The network has overcome several crises in recent years and was the most watched cable news channel for a seventh year in a row last year, well ahead of competitors like MSNBC and CNN.

Jury selection is expected to finish this week, with the trial proper expected to start Monday.

© Agence France-Presse