Lawsuits that challenge congressional redistricting plans must be allowed to follow a streamlined legal path that more quickly reaches the Supreme Court, the justices ruled Tuesday.

The Supreme Court’s unanimous decision found that a 1910 law, updated in 1976, requires such lawsuits to be heard by a three-judge panel of district court judges. The ruling reversed the U.S. Court of Appeals for the 4th Circuit based in Virginia, which had allowed one judge to determine whether a claim is too insubstantial — obviously frivolous or inescapably meritless — to need to convene a three-judge panel.

Allowing the redistricting challenges to go to a three-judge panel not only means one less step in the appeals process, but it guarantees a Supreme Court review. That legal path is often followed by voting rights challenges as well.

In the case, Shapiro v. McManus, three Maryland residents who are challenging the state’s 2011 redistricting plan had their lawsuit dismissed by one judge. The lawsuit, filed by lead plaintiff Stephen Shapiro, should have made it to a three-judge panel, the Supreme Court ruled.

Tuesday’s opinion instructs Shapiro’s case to go before a three-judge panel to hear the claim that the state’s political gerrymandering violated their first amendment rights to political association. The Supreme Court decision does not address the merits of the lawsuit.

“Perhaps petitioners will ultimately fail on the merits of their claim,” Justice Antonin Scalia said from the bench while announcing the decision, but the law “entitles them to make their case before a three-judge district court.”

Appeals in cases decided by the three-judge panel go directly to the Supreme Court, which must consider them. Cases decided by one judge must first go through the federal appeals court and then on to the Supreme Court, which can decline to hear them.

One of the highest-profile redistricting cases on the Supreme Court’s docket this year — a lawsuit over the one-person, one-vote standard — followed that legal path. The justices heard arguments on that case Tuesday.