A gun control group filed a lawsuit Thursday accusing the Justice Department of aiding gun manufacturers in skirting assault weapons laws.

The Brady Campaign to Prevent Gun Violence (search), along with the Million Mom March (search), said the Justice Department's Bureau of Alcohol, Tobacco, Firearms and Explosives allowed gun makers to replace the housing for the firing mechanism on legally owned semiautomatic assault weapons, which the groups say violates the 1994 Assault Weapon Act (search).

The law makes it illegal for a person to manufacture, transfer or possess a semiautomatic assault weapon. Weapons possessed before the law was enacted are exempt.

The Brady Campaign contends in its lawsuit that manufacturing a new housing -- or "receiver" -- is prohibited because that in effect creates a new gun, and that gun should be banned.

"By allowing gun makers to manufacture new receivers, ATF has been allowing the manufacture of new assault weapons, in contravention of the statute," the Brady Campaign said in a statement Thursday.

The suit names the Justice Department, ATF, Attorney General John Ashcroft (search), and Edgar Domenech, acting director of ATF.

Neither the Justice Department nor the ATF would comment on the litigation.

The Brady Campaign cited correspondence, gathered through the Freedom of Information Act, between the ATF and Bushmaster Firearms, a weapons manufacturer in Windham, Maine, in which the ATF outlines how to replace receivers in semiautomatic weapons.

Dennis Henigan, legal director for the Brady Campaign, said the ATF policy "ensures that many thousands of grandfathered assault weapons will remain functional for many years to come. It is a policy that allows assault weapon manufacturers to manufacture new assault weapons to replace the damaged grandfather assault weapons," he said at a press conference.

The Brady Campaign said the ATF policy of issuing new serial numbers for replacement receivers, as stated in the letter, demonstrates that the ATF is allowing semiautomatic weapon production.

The ban on assault weapons has a sunset provision and is scheduled to expire in 2004. The renewal of the ban was part of a gun package that did not make it through Congress earlier this month.