Republican Senator Josh Hawley introduced a bill on Wednesday which would strip tech giants of a legal protection that means they are not liable for content posted by users.

If successful, it would make the likes of Facebook and YouTube responsible for the toxic content on their platforms, which could dramatically upend their business models.

However, companies could gain exemption from the bill if they agree to scrutiny about whether their algorithms and moderation processes are politically biased.

Republicans have pressed Silicon Valley giants on the subject of anti-conservative bias since last year, when President Donald Trump accused Google of rigging search results against him.

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A Republican senator just took a swing at Silicon Valley by introducing a bill which could make tech giants like Facebook, Twitter, and YouTube liable for the tide of harmful content they are currently struggling to hold back.

Sen. Josh Hawley introduced the bill on Wednesday, which proposes removing tech companies' protection under Section 230 of the Communications Decency Act (CDA), which prevents them from being held responsible for any illegal content posted to their platforms by users.

The bill would only apply to companies with more than 30 million active users in the US, more than 300 million users worldwide, or more than $500 million in global annual revenue. The big players of Silicon Valley all fit comfortably into these categories.

Read more: Big tech's time of reckoning: It looks like Trump is making good on his threat to take on Google and Amazon

If successful, it could dramatically upend the business models of social media platforms like Facebook. Currently, they monitor and remove harmful content after it is posted, while Hawley's bill could mean thay have to apply this scrutiny to posts before they go live, or risk being held liable for anything illegal or libellous.

Stripping big tech of its protection under the CDA has garnered in popularity on both sides of the aisle. House Speaker Nancy Pelosi told Recode's Kara Swisher in April that the tech giants were abusing the Section 230 privilege. "It is not out of the question that that could be removed," she said.

However, Hawley's bill seems to come with a very specific goal popular among Republicans — forcing the tech giants submit themselves for review to see if their content moderation enforces any kind of political bias. The stated aim of the bill is to"encourage providers of interactive computer services to provide content moderation that is politically neutral."

Under the terms of the bill, companies could be granted immunity from liability so long as they obtain certification from the FTC that their algorithms and content moderation are not politically biased. They would have to reapply for this certification every two years.

Over the past year, the Republican party has been vehement in questioning big tech companies over whether they have an anti-conservative bias. In August last year, President Donald Trump accused Google of rigging search results to surface more critical articles about him. Last month, Trump said at a White House press conference that Facebook and Twitter discriminate against conservatives.

Fellow Republicans have similarly taken up the line of attack. In April, Sen. Ted Cruz accused Facebook and Google of "censor[ing] political speech" during a Senate Judiciary subcommittee hearing.

The tech giants deny that they build anti-conservative bias into their platforms and President Trump's initial accusation that Google rigs search results against him was unsubstantiated.