A Wisconsin golf course owner who advertised nine holes of golf for $9.11 to mark the anniversary of the Sept. 11 terrorist attacks apologized Tuesday.

Tumbledown Trails Golf Course advertised the special in a newspaper Monday, saying it was intended to commemorate the 12th anniversary of the attacks that killed nearly 3,000 people.

News of the offer spread on social media and the golf course’s Facebook page was overrun with negative comments. Owner and general manager Marc Watts said he received death threats and threats to burn down the course.

“We’re a little hurt by the fact that people are putting such a negative context on this,” Watts said. “I thought people would appreciate it.”

The promotion actually began two years ago, on the 10th anniversary of the attacks, and until now was warmly received as a way to ensure people never forget the tragedy, Watts said.

But after the ad circulated on social media this year, Watts said the club’s phone began ringing off the hook.

Watts apologized Monday night on Facebook and was personally fielding calls on Tuesday, saying there was no intention to cause offense. He considered closing the course today because of safety concerns but decided to keep it open.

“We could close, but then all these people with their negative attitudes, they win,” he said.

As the father of a firefighter who died in the attack, Lee Ielpi, president and co-founder of the 9/11 Tribute Center in New York, said he understands the backlash from the ad. As for himself, though, “I don’t feel slighted,” he said.