Bills aimed at restricting sales of violent games to minors are the latest salvo in a long campaign by detractors and some parent groups to limit access to games with adult content. Critics of violent games often cite research suggesting that such games can increase aggressive behavior in young boys.

The battle over controversial video game content flared anew this summer when game publisher Take-Two Interactive Software Inc. pulled its blockbuster title "Grand Theft Auto: San Andreas" from store shelves following the discovery of hidden sex scenes in its code.

Trade groups representing the $10 billion U.S. video game industry have sued to strike down the new California law and are fighting similar battles in Michigan and Illinois.

Courts already have blocked such legislation in Washington State, the city of Indianapolis and St. Louis County in Missouri, finding that the laws violated free speech guarantees in the U.S. Constitution. Video game industry groups already have Diaz de la Portilla's bill in their sights."The Senator's proposal is clearly unconstitutional," Gail Markels, senior vice president and general counsel of the Entertainment Software Association, said in a statement.

But lawmakers, who grab headlines for taking on the makers of violent games, are undaunted and U.S. Sen. Hillary Clinton is leading a battle on the federal front.