Chief executive Jack Dorsey said Twitter will "continue to point out incorrect or disputed information about elections globally" after US President Donald Trump threatened action against the platform for adding fact-checking links to his tweets about postal votes.
White House officials said Mr Trump would sign an executive order on social media companies on Thursday, without offering details. The Republican president threatened to shut down websites he accused of stifling conservative voices.
The dispute erupted after Twitter on Tuesday for the first time tagged Mr Trump's tweets about unsubstantiated claims of fraud in mail-in voting with a warning prompting readers to fact check the posts.
Mr Dorsey defended the company's action in a series of posts on Wednesday and said the policy would continue.
"This does not make us an 'arbiter of truth'," he wrote. "Our intention is to connect the dots of conflicting statements and show the information in dispute so people can judge for themselves. More transparency from us is critical so folks can clearly see the why behind our actions."
Mr Trump's posts about California's vote-by-mail plans "may mislead people into thinking they don't need to register to get a ballot", he said.
Separately, a three-judge panel of the US Court of Appeals in Washington on Wednesday upheld the dismissal of a lawsuit by a conservative group and right-wing YouTube personality against Google, Facebook, Twitter and Apple accusing them of conspiring to suppress conservative political views.
In an interview with Fox News Channel on Wednesday, Facebook's chief executive, Mark Zuckerberg, said censoring a platform would not be the "right reflex" for a government worried about censorship. Fox played a clip of the interview and said it would be aired in full on Thursday.
Facebook left Mr Trump's post on mail-in ballots on Tuesday untouched.
The American Civil Liberties Union said the First Amendment of the US Constitution limits any action the president could take.
Facebook and Alphabet's Google declined comment. Apple did not respond to a request for comment.
"Republicans feel that Social Media Platforms totally silence conservatives voices. We will strongly regulate, or close them down, before we can ever allow this to happen," Mr Trump said in posts on Twitter on Wednesday.
"Clean up your act, NOW!!!!"
Mr Trump, who is seeking re-election this November, has more than 80 million followers on Twitter and uses the platform to connect directly with his support base.
"Big Tech is doing everything in their very considerable power to CENSOR in advance of the 2020 Election," he tweeted. "If that happens, we no longer have our freedom."
Mr Trump's threat is his strongest yet within a broader conservative backlash against Big Tech. Shares of both Twitter and Facebook fell on Wednesday.
Last year the White House circulated drafts of a proposed executive order about anti-conservative bias which never gained traction.
The Internet Association, which includes Twitter and Facebook among its members, said online platforms do not have a political bias and they offer "more people a chance to be heard than at any point in history".
Twitter said Mr Trump's tweets were labelled as part of efforts to enforce the company's "civic integrity policy."
The policy document on Twitter's website says people may not use its services for manipulating or interfering in elections or other civic processes.
In recent years Twitter has tightened its policies amid criticism that its hands-off approach allowed fake accounts and misinformation to thrive.
Tech companies have been accused of anti-competitive practices and violating user privacy. Apple, Google, Facebook and Amazon face antitrust probes by federal and state authorities and a US congressional panel.
Republican and Democratic lawmakers, along with the US Justice Department, have been considering changes to Section 230 of the Communications Decency Act, a federal law largely exempting online platforms from legal liability for the material their users post. Such changes could expose tech companies to more lawsuits.
Republican Senator Josh Hawley, a frequent critic of Big Tech companies, sent a letter to Mr Dorsey asking why Twitter should continue to receive legal immunity after "choosing to editorialise on President Trump's tweets".