The social platform Parler is suing Amazon after the tech giant's web division forced the conservative-friendly network offline for failing to rein in incitements to violence.
Nevada-based Parler asked a federal court for a restraining order to block Amazon Web Services from cutting off access to internet servers.
The suit comes amid a wave of action by online giants blocking access to supporters of US President Donald Trump in the wake of last week's US Capitol invasion and purported plans for new violent demonstrations, especially on the day President-elect Joe Biden is due to take office.
The lawsuit said Parler was due to go dark tonight, but web trackers said it already was offline early in the day and had failed to find a new hosting service.
Shutting down the servers would be "the equivalent of pulling the plug on a hospital patient on life support," the lawsuit said. "It will kill Parler's business - at the very time it is set to skyrocket."
Parler alleged Amazon was violating antitrust laws and acting to help social rival Twitter, which has banned Mr Trump and other accounts promoting violent actions.
"AWS's decision to effectively terminate Parler's account is apparently motivated by political animus. It is also apparently designed to reduce competition in the microblogging services market to the benefit of Twitter," the complaint said.
Amazon did not immediately reply to a request for comment.
In a series of posts on Parler before the site went down, CEO John Matze accused the tech giants of a "war on free speech."
Mr Matze also denied allegations that it enables violent content.
"Our team worked hard to produce a strong set of community guidelines, which expressly forbids content which incites or threatens violence, or other activity which breaks the law," he said in a statement.
However he also maintained that it is problematic to police all content because "Parler is not a surveillance app, so we can't just write a few algorithms that will quickly locate 100 percent of objectionable content."
The lawsuit is the latest twist in a tussle between online operators and supporters of the president which hit a new phase after the siege of the US Capitol last week.
Twitter and Facebook each suspended Mr Trump's account, while online payment service Stripe said it would stop handling transactions on Mr Trump's website following last week's assault.
Parler, which launched in 2018, operates much like Twitter, with profiles to follow and "parleys" instead of tweets.
In its early days, the platform attracted a crowd of ultraconservative and even extreme-right users. But more recently it has signed up many more traditional Republican voices.
Supporters of Mr Trump have expressed outrage at the news the platform was being taken down.
Ahead of the shutdown, the president's son, Donald Trump Jr, complained that "big tech has totally eliminated the notion of free speech in America."
The platform drew fierce criticism in 2018 when investigators found that the shooter who killed 11 people in an attack on a Pittsburgh synagogue had earlier posted anti-Semitic messages on the site.