FREDERICKSBURG — In a radio commercial for concealed handgun classes, instructor Crockett Keller is heard telling listeners that he'll accept cash, credit cards, checks, gold or used guns as their $100 payment.

But it's what Keller won't accept that has created a rhetorical firefight on talk shows and which has gone viral on the Web.

“If you are a socialist liberal and/or voted for the current campaigner-in-chief,” Keller says in the 1-minute, 7-second ad, which aired several times last week in the Hill Country town of Mason, “please do not take this class. You've already proven that you cannot make a knowledgeable and prudent decision as required under the law. Also, if you are a non-Christian Arab or Moslem (sic), I will not teach you this class. Once again, with no shame, I am Crockett Keller.”

That last sentiment is spelled out in capital letters on a yellow sign that will be hanging today on Keller's table at the Texas Gun and Knife Show at the Gillespie County Fairgrounds: “If you are Muslim and will not pledge allegiance to the United States of America, I will not sell you any firearm or accessory.”

Since the brief spot aired on Mason's KHLB, it has been turned into several YouTube clips, which together have logged more than 20,000 views. He says he has received about 1,000 phone calls. Nearly all have been supportive. A few have come from respectful dissenters.

Friday, however, Keller's wife, Diane, played back two threatening recorded messages, including one in which a caller claimed to be Muslim and threatened to kill the Kellers. Sheriff's deputies are investigating both calls.

TOM REEL/SAN ANTONIO EXPRESS-NEWS

The affable Keller, 65, who typically sports a wide-brimmed straw hat, isn't scared by the death threats, saying they vindicate his position.

“And that's exactly why I won't teach” Muslims, he said, setting up his booth Friday at the gun show. “Actually, I don't have a problem with them, but I think I'm getting one. That's OK. I guess turnabout is fair play.”

Just then, another gun dealer walked up to Keller and offered his hand.

“I want to shake your hand,” said the 60-year-old retiree from Comfort, who declined to identify himself for publication. “Thanks for what you said. You spoke for all of us.”

Keller says the ad isn't just about his frustration with current events. His refusal to teach certain people, he says, fits in with his interpretation of state law, which gives him latitude in denying instruction to people who don't appear mentally fit or capable of making good decisions with a firearm.

His concerns, he says, arose after the 2009 Fort Hood shooting spree that left 13 dead and 29 injured. Army Maj. Nidal Malik Hasan, an American-born Muslim, is charged in connection with that incident.

Given the constant stream of terrorism threats from groups with Middle Eastern ties, Keller says, he can't act in good conscience by training any Muslim to legally carry a firearm.

Nor will he offer his instruction to anyone who admits voting for President Barack Obama.

“How can I trust that a person who made that mistake — who had 2½ years to vet the man and still voted for him — will make a rational, prudent and sane decision” when to use a firearm?” he asks. “I can't.”

He says the ad's caveats were made tongue-in-cheek and that he hasn't yet had to turn down anyone.

Not everyone sees it as a joke.

Sarwat Husain, president of the San Antonio chapter of the Council on American-Islamic Relations, pointed out the irony of Keller's commercial, which she says promotes the usage of a device with the sole purpose of killing.

“We're not missing anything,” she said. “I'm happy he's not selling to the Muslims. Because that blood is on the hands of this guy. He's a racist and he's a bigot. He can keep his guns and he can promote killing.”