(CNN) -- The small, black-and-white newspaper ad offered a discount: Nine holes of golf for $9.11 -- on September 11.
The management of a Wisconsin golf course said the idea was to remember the victims of the September 11, 2001, attacks, but the ad turned into a public relations disaster on social media.
By Tuesday, TumbleDown Trails Golf Course was reporting death threats.
The golf course in Verona, Wisconsin, placed an advertisement in Monday's Wisconsin State Journal offering to "commemorate" the 12th anniversary of the terror attacks with "9 holes with cart for only $9.11 per person or 18 holes with cart for only $19.11!"
The ad quickly began circulating on social media, and the golf course's Facebook page was flooded with angry comments.
"It's an abomination and a disgrace," one commenter wrote.
"To make an opportunity out of a national tragedy is outrageous," another said.
The management of the course posted an apology on Facebook Tuesday and on a recorded message on the course's main phone line.
"Please accept our sincere apologies," the recording said. "Our attempt to remember the tragedy of that day has been met with negativity and now even death threats. We ask that you please take a moment to reflect and remember those we lost that day, as we were trying to do."
By Tuesday afternoon, many Facebook commenters were defending the course. Some called the ad an honest mistake, and some said outsiders were pumping up the outrage.
"They shouldn't have to apologize for anything! Who are you people to judge," one commenter wrote. "I've played the course before. Nice staff and seem like good people."
Another called the ad "badly worded, ill thought out" but added, "I'm not any more offended than I have been throughout the years every time I see a 9/11 limited edition coin on TV or exploding towers with an eagle crying on a T-shirt or ... the hundreds of others exploiting a tragedy for profit."
A message left on the course's voice mail was not returned Tuesday. Management said in a Facebook post the course may be closed Wednesday because of security concerns.