The US Supreme Court raised the legal bar for prosecutors pursuing obstruction charges against defendants involved in the January 6, 2021, attack on the Capitol in a ruling on Friday with potential implications for the federal criminal case against Donald Trump for trying to undo his 2020 election loss.

The justices ruled 6-3 to throw out a lower court’s decision that had allowed a charge of corruptly obstructing an official proceeding — the congressional certification of President Joe Biden’s victory over Trump that the rioters sought to prevent — against defendant Joseph Fischer, a former police officer. The justice directed the lower court to reconsider the matter.

The court, in the decision authored by Chief Justice John Roberts, ruled that an obstruction conviction requires prosecutors to show that a defendant “impaired the availability or integrity” of documents other records related to an official proceeding — or attempted to do so.

Roberts was joined by fellow conservative Justices Clarence Thomas, Samuel Alito, Neil Gorsuch and Brett Kavanaugh, as well as liberal Justice Ketanji Brown Jackson. Roberts rejected the justice department’s more expansive reading of what constitutes obstruction, calling it “a novel interpretation (that) would criminalise a broad swathe of prosaic conduct, exposing activists and lobbyists alike to decades in prison”.