By Kaya Yurieff and Brian Fung, CNN Business

(CNN) -- A Senate Commerce Committee hearing with the CEOs of Facebook, Google and Twitter is underway on Wednesday amid cries of conservative bias and threats to change a crucial law, known as Section 230, that protects the companies' ability to moderate content as they see fit. The tech CEOs appeared via video.

The hearing comes less than a week before the US election and as social media companies have been bracing for an onslaught of misinformation. In recent days, Facebook and Twitter have both taken action to slow the spread of some content, bringing about allegations of bias, censorship and even election interference.

Sen. Roger Wicker opened Wednesday's hearing by slamming the tech companies for an "apparent double standard" that disadvantages conservative content on social media. Wicker said that Section 230, which shields tech companies from litigation over their content moderation decisions, must be changed. "The time has come for that free pass to end," he said.

Sen. Maria Cantwell, the top Democrat on the Senate Commerce Committee, said she hoped Wednesday's hearing would not cause a "chilling effect" on tech companies' efforts to reduce misinformation, particularly around the election and Covid-19.

Google CEO Sundar Pichai said the company approaches its work without political bias, "full stop."

"To do otherwise would be contrary to both our business interests and our mission, which compels us to make information accessible to every type of person, no matter where they live or what they believe," Pichai said.

At the heart of the hearing is Section 230 of the Communications Decency Act. The companies have invoked the federal law in one court case after another to dismiss potentially costly lawsuits over messages, videos and other content created by users.

Under Section 230, "interactive computer services" are considered legally separate from the users who generate their content. They can't be said to publish or "speak" the words of their users. In practice, courts have repeatedly accepted Section 230 as a defense against claims of defamation, negligence and other allegations.

In his opening remarks, Dorsey said restricting Section 230 could stifle startup innovation and further the dominance of large tech companies. Dorsey proposed that Section 230 be expanded to require that companies provide clear explanations of their content moderation decisions, a "straightforward" appeals process and the ability for consumers to choose the algorithms that serve up social media content.

Facebook CEO Mark Zuckerberg highlighted the importance of Section 230 in his opening remarks, but said lawmakers have a role to play in determining what content is acceptable, too, and that's why he's called for increased regulation in the past. Zuckerberg said Facebook looks to be "fair and consistent" in its policies and decision making amid complaints from both parties that the company doesn't moderate its platform appropriately.

In a video released ahead of the hearing, the Senate Commerce Committee highlighted what it says are examples of social platforms' actions against conservative accounts, such as Twitter labeling a tweet from Fox News personality Tucker Carlson, saying the media he shared included "potentially sensitive content."

Independent studies of social media have found little credible evidence to suggest that the technology is biased against right-wing viewpoints.

Attacks on Section 230 have escalated in recent days as Facebook and Twitter limited the distribution of a series of articles by the conservative-leaning New York Post that claimed it obtained "smoking-gun" emails about Hunter Biden, the son of Democratic presidential nominee Joe Biden, and his dealings in Ukraine. CNN has not determined the authenticity of the emails.

Facebook said it decided to "reduce distribution" of the article "pending fact-check review" as part of its policy against "misinformation." Twitter later blocked users from tweeting links to the main story as part of its policy against spreading "hacked materials," even though it wasn't clear whether the underlying emails attributed to Hunter Biden were hacked, copied, or fabricated.

US authorities are investigating whether the recently published emails are connected to an ongoing Russian disinformation effort targeting the former vice president's campaign, a US official and a congressional source briefed on the matter said.