The prosecutors exceeded their authority when they brought the January 6 rioters to court for obstruction of the certification of the 2020 presidential election, the US Supreme Court believes.
The decision may result in dozens of verdicts being overturned.
The judges believe that "obstruction" should be interpreted more narrowly and mean that the accusation of hindering an official procedure must contain evidence that the defendant attempted to manipulate or destroy documents.
In the statement, Chief Justice John Roberts writes that the prosecutors' interpretation of the law would "criminalize a broad spectrum of prosaic behavior, which would expose activists and lobbyists to decades in prison".
The case was brought to the Supreme Court in the case of a former police officer, also a supporter of former President Donald Trump, who stormed the Capitol building along with hundreds of others on January 6, 2021.
The Supreme Court's decision means that the case of the former police officer will be sent back to a lower court, which will decide whether the charges against him can stand in light of the Supreme Court's narrower interpretation of "obstruction".
In total, over 50 rioters have been convicted of obstruction, with nearly 30 still in prison.
The case also has potentially significant consequences for Donald Trump, who faces four charges related to the storming of the Capitol. The investigation has been led by special prosecutor Jack Smith.
