The Supreme Court on Thursday struck down Minnesota’s ban on political apparel worn by voters when they cast ballots as a violation of the First Amendment, ruling that the state’s definition of what can’t be worn at the polling place is too vague.

In a 7-2 opinion, the majority found that while the state’s election judges can strive to enforce the statute in an evenhanded manner when they decide what is political when they screen individuals at the entrance to polls, there are no “objective, workable standards.”

“Without them, an election judge’s own politics may shape his views on what counts as ‘political,’” Chief Justice John G. Roberts Jr. wrote for the majority. “And if voters experience or witness episodes of unfair or inconsistent enforcement of the ban, the State’s interest in maintaining a polling place free of distraction and disruption would be undermined by the very measure intended to further it.”

The century-old Minnesota law, similar to those in about nine other states, prohibited voters from wearing clothes with political messaging related to an election or ballot question as an effort to keep the dignity, decorum and solemnity of polling places.

At oral arguments in February, the justices went through several hypotheticals, such as voters who want to wear a “Make America Great Again” hat, a “#resist” T-shirt, or a “Parkland Strong” button.

The majority made clear that a state can reasonably decide to ban some forms of advocacy from polling places, and Minnesota can choose to prohibit certain apparel because of the message it conveys.

“Casting a vote is a weighty civic act, akin to a jury’s return of a verdict, or a representative’s vote on a piece of legislation,” Roberts wrote. “It is a time for choosing, not campaigning.”

But it pointed to laws in states such as California and Texas that ban displays “in more lucid terms,” while fair enforcement of Minnesota’s law would require an election judge “to maintain a mental index of the platforms and positions of every candidate and party on the ballot.”

Would a “Support Our Troops” shirt be banned if one of the candidates or parties had expressed a view on military funding, Roberts wrote, or a “#MeToo” shirt referencing the movement to increase awareness of sexual harassment and assault?

If a state wants to “set its polling places apart as areas free of partisan discord, it must employ a more discernible approach than the one Minnesota has offered here.”

Joining Roberts in the majority were Justices Anthony M. Kennedy, Clarence Thomas, Ruth Bader Ginsburg, Samuel A. Alito Jr., Elena Kagan and Neil Gorsuch.

Justice Sonia Sotomayor wrote a dissent, joined by Justice Stephen G. Breyer, because the Supreme Court issued the decision before the Minnesota state courts had a chance to rule on the ban, “which likely would obviate the hypothetical line-drawing problems that form the basis of the Court’s decision today.”

The voters who brought the case wanted to wear a “Tea Party Patriots” shirt or a button with the words “Please I.D. Me” — a reference to a contentious issue over voter identification laws — and a telephone number for election reform groups.

The case is Minnesota Voters Alliance v. Mansky, Docket No. 16-1435.