The AR-15 — the gun used in the Newtown shooting, and the sale of which would banned under Maryland's new law — is the nation's best-selling rifle.
Maryland's Attorney General Douglas F. Gansler has rebutted the NRA's argument that the law is so broadly written that it violates the Second Amendment.
In late March, an NRA affiliate and the New York State Rifle and Pistol Association filed a lawsuit with several other New York gun groups arguing that that state's new gun law prohibiting commonly possessed guns and magazines violates the Second Amendment. A New York federal judge declined to stop that state's law from taking effect.
National and local debate on gun control has spurred record gun sales in Maryland, and overwhelmed the state's system for background checks. Gun rights groups have filed two lawsuits against the Maryland State Police over a months-long delay in background checks and the agency's efforts to resolve them.
Thursday's lawsuit is the first constitutional challenge to the new Maryland law.
The gun-rights advocates cite a 2008 Supreme Court case involving gun laws in the District of Columbia, in which the court struck down many restrictions as unconstitutional and held that handguns were the "arms" cited in the Second Amendment.
Gansler sent a 25-page letter to Gov. Martin O'Malley in May laying out the legal defense for the constitutionality of the law.
"Senate Bill 281 was crafted carefully to balance the rights of legitimate gun owners with the need for increased public and law enforcement safety from gun violence," Gansler wrote. "We are confident that the resulting legislation is constitutional and legally defensible."
Staff writer Ian Duncan contributed to this report.