April 5 (Reuters) - The U.S. Supreme Court on Monday brought an end to a legal fight over former President Donald Trump's effort to block critics from following his now-frozen Twitter account, deciding the dispute was moot and throwing out a lower court's decision that found he had violated constitutional free speech rights.
None of the justices on the court, which has a 6-3 conservative majority, dissented from Monday's action. But conservative Justice Clarence Thomas wrote a separate opinion echoing concerns made by Republicans about the power of social media companies like Twitter, saying the court needs to step in.
"We will soon have no choice but to address how our legal doctrines apply to highly concentrated, privately owned information infrastructure such as digital platforms," Thomas wrote.
Thomas said social media companies, which under U.S. law have leeway as private entities to moderate user content as they see fit, might have to be treated more like businesses that are subject to public accommodation laws, which require all customers to be treated equally.
Trump had appealed after the New York-based 2nd U.S. Circuit Court of Appeals concluded that he had violated the U.S. Constitution's First Amendment by blocking his critics on the social media platform. Trump, a Republican, left office in January, replaced by Democratic President Joe Biden.
With Trump no longer president, the justices declined to hear arguments and resolve the case on the merits, tossing out the 2nd Circuit decision.
Throughout his presidency, Trump had regularly used Twitter to promote his agenda and attack detractors. Twitter banned Trump from its service days after a mob of his supporters attacked the U.S. Capitol in a deadly riot on Jan. 6.
Republicans and Democrats both have criticized social media companies but often for different reasons, with Republicans saying these platforms have discriminated against conservatives while Democrats contend that the companies have not done enough to remove disinformation and extreme content.
Some Republicans have called for the companies to be stripped of legal protections they are accorded under a measure called Section 230 of the Communications Decency Act. The law gives companies immunity over content posted on their sites by users.
Trump made his innumerable posts on the Twitter Inc social media platform an important way of communicating both before and during his presidency.
Before his permanent suspension, Trump's @realDonaldTrump account, which he opened in 2009, had more than 88 million followers. Twitter said it expelled Trump from its platform "due to the risk of further incitement of violence."
Trump touted his use of social media as a way to bypass traditional news media outlets, which he has called "fake news" while referring to journalists as the "enemy of the people."
The case began when seven people who Trump had blocked in 2017, along with the Knight First Amendment Institute at Columbia University, challenged Trump's power to exclude people with whom he disagreed from his Twitter account.
One of the blocked people had criticized Trump's travel ban targeting people from several Muslim-majority countries. Another had objected to Trump's promotion of a new coal mine, writing, "Congrats and now black lung won't be covered under #TrumpCare." Trump's administration had said some blocked users had used inflammatory language.
The 2nd Circuit's ruling upheld a federal judge's 2018 decision against Trump, which prompted the president to unblock some accounts.
(Reporting by Andrew Chung in New York and Lawrence Hurley in Washington; Editing by Will Dunham)