COLUMBUS — U.S. Senate candidate P.G. Sittenfeld and anti-gun activists today launched a constitutional amendment campaign to restore the right of cities such as Toledo to enact local gun laws that are stricter than state law.

They concede that the effort would likely be extremely expensive and manpower intensive and may not come together in time for the 2016 general election ballot. But Mr. Sittenfeld vowed to stick with it, regardless of whether he will be on that ballot.

The proposed amendment would restore the home-rule authority of local governments to act when it comes to guns only, an authority that was significantly weakened in 2006 when lawmakers passed a state law prohibiting gun laws that are more restrictive than state or federal law.

“After the Ohio Supreme Court upheld that law, Cleveland’s ban on assault weapons went out the door,” Mr. Sittenfeld said. “So did Columbus’, which pleased then Gov. (Ted) Strickland, who publicly criticized the assault weapons ban and said he opposed it.

“Toledo and Clyde were forced to allow guns to be brought into their city parks,” he said. “And all Ohioans everywhere lost part of their autonomy, and, at least where guns are concerned, are now required to do what Columbus tells them to do.”

Mr. Sittenfeld, currently a Cincinnati city councilman, has made gun violence a major issue as he campaigns for the Democratic nomination for the right to take on Republican U.S. Sen. Rob Portman in November. He will face the Ohio Democratic Party-endorsed Ted Strickland in the March 15 primary election.

His gun positions have largely mirrored those of Democratic presidential candidate Hillary Clinton. And while Mr. Strickland is backing Ms. Clinton, he has been a gun-rights advocate. He was endorsed by the National Rifle Association in his unsuccessful re-election bid in 2010 against Republican John Kasich.

Mr. Sittenfeld said he would welcome Mr. Strickland’s signature among the roughly 306,000 the new organization would have to gather in order to appear on the Nov. 8 ballot.

“I’ll ask him,” said Toby Hoover, founder of the Toledo-based Ohioans Against Gun Violence.

The group hopes to submit proposed petition summary language for Attorney General Mike DeWine’s approval by early March in hopes of hitting the streets soon after to gather the valid signatures of registered voters to put the question on the ballot.

Mr. Sittenfeld said the amendment would allow cities to pass ordinances such as banning assault-style weapons or limiting where firearms may be carried. But he does not believe local laws could be used to ban guns altogether within their boundaries in violation of the Second Amendment of the U.S. Constitution or to completely override state law allowing the carrying of concealed handguns.

Gary Witt, one of the directors of Ohioans for Concealed Carry, said he hopes the effort goes nowhere.

“The patchwork laws that had been in various communities had done nothing but cause problems for gun-owners,” he said. “They never knew from one city to another what the law was. Unfortunately, that made criminals out of honest law-abiding citizens. We are definitely against this, and we will work against it.”

First Published January 28, 2016, 5:46 p.m.