WASHINGTON (AP) -- States across the country are stiffening penalties for domestic violence assaults that involve attempts to strangle someone.

Choking is a common act of domestic violence, but it's hard to prove because victims are often left with few, if any, signs of physical injury. The result is that many attempted strangulation cases have been handled as misdemeanors.

But anti-domestic violence organizations are leading the charge in the other direction.

About 30 states have passed laws, most in the past decade, making it a felony under certain circumstances to knowingly impede a person's breathing or airways. South Dakota, Iowa and Tennessee are among recent states to act, and Virginia's governor signed a law last week.

Some opponents question if the laws are necessary and fear they could lead to excessive prosecution.