In a decision free speech advocates celebrated as a "historic moment for the First Amendment" and online freedom of expression, a federal judge ruled (pdf) on Wednesday that President Donald Trump cannot block Twitter users for their political views or criticism of his policies.

"We're pleased with the court's decision, which reflects a careful application of core First Amendment principles to government censorship on a new communications platform," said Jameel Jaffer, executive director of the Knight First Amendment Institute, a free speech advocacy group that brought the "groundbreaking" case on behalf of seven individuals Trump has blocked from seeing his Twitter posts.

"The president's practice of blocking critics on Twitter is pernicious and unconstitutional, and we hope this ruling will bring it to an end," Jaffer added.

In her opinion issued on Wednesday, U.S. District Court Judge Naomi Reice Buchwald agreed with the Knight Institute's argument that Trump's Twitter feed qualifies as a "public forum," and argued that blocking users from viewing and interacting with the president's frequent posts and tirades simply because of their political views is a violation of users' First Amendment rights.

"The viewpoint-based exclusion of the individual plaintiffs from that designated public forum is proscribed by the First Amendment and cannot be justified by the president's personal First Amendment interests," Buchwald wrote. "Because no government official is above the law and because all government officials are presumed to follow the law once the judiciary has said what the law is, we must assume that the president and [White House social media director Dan] Scavino will remedy the blocking we have held to be unconstitutional."

The Knight Institute's lawsuit, filed last July, took on particular significance as it could be one of many cases that "help society interpret free speech and First Amendment in [the] digital age," Alberto Ibarguen, CEO of the James L. Knight Foundation, noted in a tweet on Wednesday.

Katie Fallow, a senior staff attorney at the Knight Institute who led oral arguments in the case, said the court's application of the First Amendment to the president's habit of blocking users on Twitter "should guide all of the public officials who are communicating with their constituents through social media."