A liberal group on Friday filed a lawsuit in Michigan contending that former president Donald Trump is disqualified from regaining his old job based on a rarely used, post-Civil War provision in the U.S. Constitution.

This is the first time an organization with significant legal resources has sought to block the GOP frontrunner’s campaign in a swing state.

Free Speech For People argued that Trump’s attempt to overturn his 2020 election loss and encouragement of the Jan. 6, 2021 attack on the U.S. Capitol violated section three of the 14th Amendment, which holds that anyone who swore an oath to uphold the constitution and then “engaged in insurrection or rebellion” against it is barred from holding office.

The case is the second the organization has filed to block the GOP presidential frontrunner’s bid, following one in Minnesota.

Dozens of cases have been filed nationally but the Free Speech For People cases and one filed in Colorado by another liberal group are the first brought by organizations with significant legal resources.

Those are seen as most likely to reach the U.S. Supreme Court, which has never ruled on the provision.

Michigan is a particularly significant location for a challenge because it is both a swing state and its Democratic Secretary of State, Jocelyn Benson, wrote in The Washington Post earlier this month that she and other top election officers don’t have the ability to bar Trump under the clause.

Section three has only been used a handful of times since the Civil War.