The Supreme Court ruled on Friday that federal prosecutors had improperly used an obstruction law to prosecute some members of the pro-Trump mob that stormed the Capitol on Jan. 6, 2021.

The ruling could affect the prosecutions of hundreds of rioters out of the more than 1,400 who have been charged with an array of offenses for taking part in the effort to block certification of the 2020 election results.

It could also have an effect on part of the federal case against former President Donald J. Trump accusing him of plotting to overturn his 2020 loss at the polls. But the precise impact on those cases will not become clear until trial courts review them in light of the Supreme Court’s ruling.

Prosecutors had argued that the law applied to efforts to obstruct an “official proceeding” — the joint session of Congress that took place on Jan. 6, 2021, to certify the Electoral College results.

But Chief Justice John G. Roberts Jr., writing for the majority, read the law narrowly, saying it applied only when the defendant’s actions impaired the integrity of physical evidence.

Lower courts will now apply that strict standard, and it may lead them to dismiss charges against some defendants, although most of those charged or convicted under the obstruction law also face other charges.