A supporter of the amendment in Cabarrus County, about 20 miles northeast of Charlotte, showed himself in a YouTube video firing a shotgun twice at a neighbor's lawn sign that encouraged people to vote against the amendment, a United Press International review of the video indicated.
"That's how we deal with it around here," said the man, who identified himself in the video as Alex Wylde.
Anti-amendment voter Cameron Hughes, 25, told The (Raleigh) News & Observer he considered the amendment "an embarrassment" and "pathetic."
"I'm ashamed to have to come out here and vote on something like this, and, if the polls are right, I'm ashamed that apparently a large majority of the citizens of my state are pro-bigotry," he said.
Campaigners for and against the amendment -- which passed 61 percent to 39 percent Tuesday -- called a steady stream of complaints into the Wake County Board of Elections in Raleigh in the day, each side complaining about the opponents' alleged illegal electioneering.
"I've never seen anything like this," county Deputy Elections Director Gary D. Sims told the newspaper.
The North Carolina amendment declares "marriage between one man and one woman is the only domestic legal union that shall be valid or recognized in this state."
Besides same-sex marriage, the amendment bans civil unions and domestic partnerships of any kind.
"We didn't want civil union to be a marriage clone," Republican state Sen. Dan Soucek, one of the amendment's primary sponsors, told Fox News Channel before the election.
"We wanted that institution to be protected, not just the word," he said.
About 12 percent of North Carolina domestic partnerships are between same-sex couples, 2010 U.S. Census data indicate.
Evangelist Billy Graham, 93, last week urged voters to support the amendment, which 11 family law professors at seven North Carolina universities said could deprive unmarried women of protections against domestic abuse, while restricting child custody and visitation rights for unmarried gay or straight couples.
North Carolina joins about 30 states in approving a constitutional amendment banning gay marriage, even as polls show the national mood is softening on the issue.
The Tar Heel State already prohibited gay marriage by statute, but amendment backers said it was important to enshrine the ban in the state Constitution so a judge or future Legislature would have a hard time overturning it.
"Marriage is the basic building block of society," Tami Fitzgerald, chairwoman of the pro-amendment group Vote for Marriage N.C., told The Wall Street Journal. "This is a decision that people should get to make."
President Barack Obama was "disappointed" by the vote, which he has called divisive and said would discriminate against gays, a spokesman said.
Six states and the District of Columbia allow same-sex marriages.
"We know that we pushed the needle forward," Jeremy Kennedy, the campaign manager for the Coalition to Protect All NC families, a group that fought the amendment, was quoted by The New York Times as saying to a group of staff members and volunteers after the vote.
"This is just a skirmish, a battle in the war that we will win," Kennedy said. "We gave everything we had."