Bartender Randy Shields was serving British brews and Arizona ambers as usual at Shady's bar in east Phoenix when he saw a customer walk in with a hunting knife strapped to his hip.

A disturbing image flashed through his mind — "that knife sliding between my ribs."

The customer willingly turned over the knife while he was in the bar, but Shields still worries about a new Arizona law that goes into effect Wednesday that will allow guns into Arizona bars and restaurants that serve alcohol.

Under the law, backed by the National Rifle Association, the 138,350 people with concealed-weapons permits in Arizona will be allowed to bring their guns into bars and restaurants that haven't posted signs banning them.

Those carrying the weapons aren't allowed to drink alcohol.

The new law has Shields and other bar owners and workers wondering: What's going to happen when guns are allowed in an atmosphere filled with booze and people with impaired judgment?

"Somebody can pull the trigger, then a bullet comes out, and people get hurt and killed," said Brad Henrich, owner of Shady's, a popular neighborhood bar that sees occasional minor scuffles. "The idea of anyone coming in with guns in a place that serves alcohol just seems ludicrous."

An 8 1/2-by-11-inch sign that says "No Firearms Allowed" and shows a red slash over a gun now hangs next to Henrich's liquor license. If a bar owner does not post such a state-approved sign, people with concealed weapons are allowed in with their guns.

There is no way to track how many of Arizona's 5,800 bars and restaurants that serve alcohol have posted such signs. The Arizona Department of Liquor Licensing and Control has signs available for download on its Web site and doesn't track that figure.

The department has provided 1,300 signs to bar and restaurant owners who went to the department in person or asked to have signs mailed to them.

A similar law took effect in July in Tennessee, with the same reaction from many bar owners who posted signs banning firearms. The NRA says 41 states now allow guns in businesses that serve alcohol.

"I hate to have to put them up," Mark DeSimone, owner of the Hidden House Cocktail Lounge in central Phoenix, said of the signs. "It looks scary. It looks to somebody like, should I go in this place because they obviously have a problem with people bringing weapons in."

DeSimone has signs banning guns next to his liquor license and outside the bar.

He said every bar owner should be concerned about the possible consequences of allowing anyone into a bar with a gun.

"You don't want people to even have a stick," he said. "When I take steak knives out (for customers), I look for the ones that don't have pointy ends."

Taking a gun into a bar banning the weapons would be a misdemeanor punishable by up to 30 days in jail and a fine of up to $500.

But the law includes a partial legal defense. A person would be exempt if the sign banning guns had fallen down, the person wasn't an Arizona resident, or the notice was first posted less than a month earlier.

J.P. Nelson, director of the NRA's western region, said people with concealed-weapons permits have the right to protect themselves by bringing guns into bars and restaurants.

"Bad things happen in bars and restaurants," Nelson said. "People want to carry a gun and if the facility owner doesn't have a problem with it, there shouldn't be a problem. If a person starts drinking and gets in a shootout and kills someone, of course they're subject to criminal prosecution."

Marc Peagler, owner of the Silver Spur Saloon Restaurant in Cave Creek outside Phoenix, said he will allow people with concealed weapons permits to carry in his business, and Silver Spur will be safer because of it.

"It's a deterrent," he said. "In the criminal element, there is some logic that says when people look at a place that they might want to rob, the ones that have big signs up that say 'We do not permit firearms' would be the first target.

"They know there's not going to be anybody in there that can stop them," he said.

Arizonans are also allowed to openly carry guns — on a belt or holster, for example. Those people still won't be allowed in bars or restaurants serving alcohol under the new law if they're armed.