PORTLAND, Maine — Gabrielle Giffords, the former congresswoman who made a remarkable recovery after being shot in the head during a 2011 mass shooting in Arizona, urged Mainers on Wednesday to vote for tighter gun control during an appearance in Portland with local Police Chief Michael Sauschuck.

The pair spoke in favor of Question 3, a measure on the November ballot that would require background checks before the private sale or transfer of guns, calling the proposal a “common sense” initiative to close loopholes in state gun law.

“Stopping gun violence takes courage. … I’ve seen great courage when my life was on the line,” said Giffords in a brief speech. “Now is that time to come together and be responsible — Democrats, Republicans, everyone.”

Giffords, who has been campaigning for tighter gun control since her recovery from the shooting, previously visited Portland in 2014 to speak about the issue. Her latest visit is part of a national tour of 14 states.

The political push for the ballot measure is being fueled by millions of dollars pumped into Maine by billionaire Michael Bloomberg through the group Everytown for Gun Safety. And the National Rifle Association has raised tens of thousands of dollars to fight the question. In August, the NRA’s executive director for legislative action, Chris Cox, visited Portland to rally opposition.

In Maine, background checks are required when purchasing a gun from a federally licensed firearm dealer. But no background check is mandated when purchasing from a private seller, such as those who frequent gun shows and sell online through websites such as Uncle Henry’s. Proponents of Question 3 say this makes it too easy for criminals and other people barred from owning firearms to get a gun.

“It’s absolutely maddening to me that we’re essentially giving away deadly weapons in that scenario without any kind of documentation whatsoever,” said Sauschuck. “That can’t stand, and that cannot continue.”

But opponents of the measure say that it would create problems for Maine hunters and be difficult to enforce. Twelve of Maine’s 16 elected sheriffs have come out against Question 3, and the Maine Warden Service issued a statement this week saying that the proposed law “could make criminals out of responsible firearm owners” and “will be difficult — if not impossible — for wardens to enforce.”

The Maine Chiefs of Police Association last month called for people to vote in favor of Question 3.

While acknowledging that his department’s work is significantly different from what the warden’s do in rural Maine, Sauschuck dismissed concerns with enforcement.

“I’m confident that we’ll be able to work with whatever system is developed, like we do every day,” he said.