A new law that allows firearms in national parks and wildlife refuges went into effect Monday, but pulling the trigger is illegal in most cases.

Glacier National Park officials note hunting is illegal in the Park and recreational use of firearms is also illegal. The only instance where firing a weapon is legal is in the case of self defense or if an individual is in imminent danger.

Federal law also prohibits firearms in certain facilities, such as park visitor centers. Glacier is currently signing all facilities where guns are prohibited and will change its signs at trailheads.

In Glacier, the main reason to carry a weapon would be in defense against bear attacks. But Park managers note the numbers simply don't support the perception.

Between 2005 and 2009, Glacier visitation totaled 9.8 million.During that timeframe, three visitors were injured by grizzly bears — none of them fatally. Bear spray was not used by any of those three individuals. The Park highly recommends bear spray over weapons use.

Studies have shown that bear spray is an effective deterrent in the rare event of a bear attack in nearly every instance.

"It is important to note that Glacier National Park is in the heart of grizzly country. That is one of the reasons many people visit the park each year. We encourage park visitors to carry, and know deterrent for a charging grizzly bear," Park Superintendent Chas Cartwright said.

The new law reverses an old Reagan-era rule that prohibited guns in national parks and was pushed by the National Rifle Association. It was supported by Montana's congressional delegation. The law was a paragraph in a larger credit card reform bill passed last year by Congress.

"While big city forest administrators have been trained to think anyone with a gun is a threat, Montanans realize that in the wild of a national park, having a firearm can mean the difference between life and death," said Congressman Denny Rehberg on Monday. "We don't give up our rights to freedom of speech or freedom of the press just because we step foot into a national park, why should the right to bear arms be any different?"

The law had its genesis in the Bush Administration. The Bush Administration proposed allowing gun owners with a valid concealed weapons permit to carry weapons in parks.

But that rule change was challenged by anti-gun groups and the National Parks Conservation Association in federal court. The court agreed that the rule change deserved more scrutiny. But instead, Congress simply wrote a law that allowed all gun owners to carry weapons in national parks and wildlife refuges.

The federal law mirrors state gun laws. For example, if a state has a law that doesn't allow guns in parks, then guns would be illegal. Montana, however, does not have such a law.