The case started when members of the Minnesota Voters Alliance, which says it works to ensure “election integrity,” turned up at Minnesota polling places wearing T-shirts bearing Tea Party logos and buttons saying “Please I.D. Me.”

They were told to cover the messages and were allowed to vote even if they refused. But they risked prosecution for disobeying polls workers’ orders.

The group and two individuals challenged the law on free speech grounds, and they lost in the lower courts. A trial judge said the “Please I.D. Me” buttons were particularly problematic because they were “part of an orchestrated effort to falsely intimate to voters in line at the polls that photo identification is required in order to vote in Minnesota.”