PORTLAND, Ore. — A federal trial over Oregon’s voter-approved gun control measure is set to open Monday in Portland, marking a critical next step for one of the toughest gun control laws in the nation after months of being tied up in the courts.

The trial, which will be held before a judge and not a jury, will determine whether the law violates the U.S. Constitution.

It comes after a landmark U.S. Supreme Court decision on the Second Amendment that has upended gun laws across the country, dividing judges and sowing confusion over what firearm restrictions can remain on the books. It changed the test that lower courts had long used for evaluating challenges to firearm restrictions, telling judges that gun laws must be consistent with the “historical tradition of firearm regulation.”

The Oregon measure’s fate is being carefully watched as one of the first new gun restrictions passed since the Supreme Court ruling last June.

The legal battle over in Oregon could well last beyond the trial. Whatever the judge decides, the ruling is likely to be appealed, potentially moving all the way up to the U.S. Supreme Court.

Oregon voters in November narrowly passed Measure 114, which requires residents to undergo safety training and a background check to obtain a permit to buy a gun.

The legislation also bans the sale, transfer or import of gun magazines with more than 10 rounds unless they are owned by law enforcement or a military member or were owned before the measure’s passage. Those who already own high-capacity magazines can only possess them at home or use them at a firing range, in shooting competitions or for hunting as allowed by state law after the measure takes effect.

The Oregon Firearms Federation and a county sheriff filed the federal lawsuit in November, contending it violated the right to bear arms under the Second Amendment of the U.S. Constitution. Democratic Attorney General Ellen Rosenblum and former Democratic Gov. Kate Brown are named as defendants.

It was one of several lawsuits filed over the measure.

In a separate lawsuit, filed in state court in rural and sparsely populated Harney County in southeastern Oregon, Gun Owners of America Inc., the Gun Owners Foundation and several individual gun owners claimed the law violates the Oregon Constitution.

The judge presiding over that case, Harney County Judge Robert S. Raschio, in December ordered the law to be put on hold. Because the lawsuit challenged Measure 114 under the state constitution and not the U.S. Constitution, it held precedence in the state, legal experts said. A trial is scheduled for September.

Supporters of the law say it would reduce mass shootings and other forms of gun violence as well as suicides, which the Oregon Health Authority said accounts for 82% of gun deaths in the state.