Relatives of victims of the Washington sniper, who shot 10 people dead last autumn, are leading a campaign to stop the bill. Denise Johnson's husband, Conrad, was murdered in October. A bus driver, he was standing on the top step of his bus preparing for his morning route when he was shot in the back by the sniper.

Mrs Johnson has filed a lawsuit against the gun shop, Bull's eye Shooter Supply, which supplied a Bushmaster rifle to one of the two men charged in the sniper attacks as well as the gun's manufacturer. Seven other victims or families of victims are likely to join in the suit against the shop which is still selling rifles.

Yet the case may never come to court because of the bill, passed by the House of Representatives last week, which would give the gun industry immunity from almost all lawsuits. It would also make the gun industry the only sector to be protected by such legislation. The Senate is due to take up the bill after the Easter break. With 52 co-sponsors already only a Democratic filibuster can stop it.

"When I heard that Congress is seriously considering giving gun dealers special protection from suits like mine, I figured this had to be some kind of bad dream," Mrs Johnson told the New York Times. "I'm appalled that Congress can take away my rights as an American to have my day in court."

The gun industry is facing suits in almost 30 cities and counties around the country, including one put forward by the oldest civil rights organisation in the US, the National Association for the Advancement of Coloured People, which accuses it of negligently supplying criminals with guns in a way that has a disproportionate affect on African-Americans.

The gun industry claims it needs the legislation to "prevent frivolous, politically-motivated lawsuits" that could "bankrupt responsible companies by blaming them for the actions of criminals", according to the general counsel of the National Shooting Sports Foundation, Lawrence Keane.

The second amendment to the American constitution defends the right of all citizens to bear arms. "A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed," it says.

Supporters of the gun industry say that gun-control campaigners are trying to subvert the constitution by stealth, by using the courts to undermine their constitutional right to bear arms.

Gun-control campaigners say that with more than 11,000 Americans killed in gun-related incidents every year, they are trying to establish a more water-tight legal framework that will prevent guns getting into the wrong hands.

Mrs Johnson, who was not allowed to testify before the House of Representatives judiciary committee, said: "This is about making these companies do things responsibly."

Others are motivated by similar concerns. "I'm not looking to put the gun industry out of business," said David Lemongello, a police officer and the only person allowed to testify against the bill earlier this month.

Mr Lemongello is suing a pawnshop in West Virginia that sold a semiautomatic pistol which badly wounded him and a colleague when they staked out a petrol station that had been robbed. An investigation proved that the gun had been sold to a gun trafficker, James Gray, who was banned from buying a gun because he was a felon. Gray then sold the guns on the black market to the man who shot at Mr Lemongello in New Jersey.

"I believe in the right to bear arms. I own a gun. I was a police officer and a police firearms instructor. We are going after one bad dealer and one irresponsible manufacturer who didn't monitor what its dealers did," he said.