Over the last decade or two, the U.S. Supreme Court has repeatedly extended the First Amendment's formidable legal shield to the Web.

In 1997, the justices tossed out the Communications Decency Act, saying Congress could not outlaw making "indecent" material available on the Internet. Last year, the law's benighted successor met the same fate, as did a law targeting animal cruelty videos that the court rejected in April.

Today the Supreme Court hears oral arguments on whether to grant video games the same favored kind of laissez-faire treatment.

Unlike those other cases, the law in question is a California statute, not one enacted by Congress. But it's received a flurry of attention from all around the country, with everyone from conservative advocacy groups and pediatric associations saying that the law is constitutional to Microsoft, Activision Blizzard, the Motion Picture Association, and payment-processor Vindicia arguing it is not.

Sean Bersell, vice president of public policy for the Entertainment Merchants Association, which sued to overturn the California law, told CNET that upholding the California law would "open the floodgates to a whole host of pernicious legislation" around the country.

"We hope the justices will again reaffirm their commitment to the First Amendment," Bersell said.

In April, the justices agreed to review a California law that a federal appeals court struck down in February 2009, saying at the time that even children and teenagers enjoy free speech rights that are protected by the First Amendment.

California is one of a string of states that have enacted similar laws restricting minors' rights to buy violent video games--legislation that so far has been uniformly rejected by the courts. Laws in Illinois and Michigan were blocked by federal judges on First Amendment grounds in 2005, and earlier laws in Indianapolis and Missouri's St. Louis County were also shot down.

A screenshot from Postal 2 for PCs. Click image for full GameSpot slideshow on the video game, which lawyers and states have singled out in the case to be heard by the Supreme Court today.

The California law slaps anyone who sells or rents a "violent video game" to a minor with a $1,000 fine. That's defined as a game in which the player has the option of "killing, maiming, dismembering, or sexually assaulting an image of a human being" in offensive ways. Parents or guardians are still permitted to buy those games for minors.

The U.S. Supreme Court has not squarely addressed this topic, but it has said in other cases that even minors have some free-expression rights.

James Steyer, president of Common Sense Media, which helped to draft the California law, called it "a very fair and First Amendment-friendly effort to try to limit the sales of ultraviolent video games to minors."

"From the standpoint of balancing the best interests of kids with the best interests of the First Amendment, this is a reasonable case," he said.

California-based Activision Blizzard, whose portfolio includes the Call of Duty series and Guitar Hero, has told the court that the existing Entertainment Software Rating Board rating is sufficient to give parents enough information about the content of video games. The rating symbols include E (suitable for early childhood) to T (ages 13 and over), M (17 and over), and A (adults only).

The political fault lines exposed by this case have been difficult to predict in advance. Washington state, Georgia, Utah, South Carolina, and six other states filed a brief saying "quick fixes such as the California statute cause more practical and constitutional problems, in expanding unneeded regulatory activity and hindering law enforcement, than they solve."

But 11 states, including Texas and Michigan, separately argued that governments "may--consistent with the First Amendment and this court's longstanding precedents--prevent minors from buying or renting without parental approval" certain types of violent video games. (The conservative Eagle Forum, founded by Phyllis Schlafly, goes even further and says that video games "do not constitute free speech" at all.)

Although California's law doesn't target a specific game by name, lawyers for the state have singled out Postal 2, which allows players to go on murderous rampages, by name. (The Federal Trade Commission has separately targeted the makers of "Grand Theft Auto: San Andreas" for including sexually explicit content.)

The pro-regulation states also cite Postal 2, saying that the game encourages players to "burn people alive with gasoline or napalm," "decapitate people with shovels and have dogs fetch their severed heads," and "kill bald, unshaven men wearing pink dresses."

California attorney general and gubernatorial candidate Jerry Brown, a Democrat, has said the state should be able to place "reasonable restrictions on the distribution of extremely violent material to children."

The Entertainment Software Association, a Washington, D.C.-based trade group that filed many of the lawsuits and has posted many of the legal documents online, says it thinks the justices will agree with the lower courts.

"We're hopeful that the court will uphold the lower court's ruling," said ESA spokesman Dan Hewitt. It's important for video game players to sign up for the Video Game Voters Network, he added. (The VGVN is currently organizing a mail-in protest against state Sen. Leland Yee, a Democrat who represents part of San Francisco and sponsored the California law.)

California Gov. Arnold Schwarzenegger signed the law in October 2005, but a federal judge blocked (PDF) it from taking effect a few months later. The U.S. Ninth Circuit Court of Appeals upheld that decision.

One reason why the case has attracted an unusual amount of attention is that the Supreme Court's recent rulings, including the Citizens United decision, have been generally pro-free speech. Unless the court wanted to nudge First Amendment law in a more restrictive direction, the thinking goes, there would be no reason for it to accept the case in the first place.

Another reason is the precedent set by this case, Schwarzenegger v. Entertainment Merchants Association, could have repercussions far beyond video game producers, gamers, and retailers.

Which is why groups as diverse as the Comic Book Legal Defense Fund and the Future of Music Coalition are siding with the video game industry. The coalition warns that if the California law is upheld, it "would lead inexorably to the enactment of new statutes prohibiting violent depictions or descriptions in other artistic media" as well.

Update 10:45 a.m. PT: Here's a report from SCOTUSblog saying that, based on the oral arguments, "the court appeared poised to nullify" California's law. The Wall Street Journal reported that "several justices suggested the law violated free-speech protections of the First Amendment." But CNN.com believes it's a closer call, with the justices appearing "genuinely torn as they heard oral arguments." (Unfortunately, I'm at a privacy conference in Canada today and couldn't be at the Supreme Court.)

Update 11:30 a.m. PT: The transcript (PDF) of the oral argument is online. It doesn't clearly show either side as prevailing, but it does seem like the justices reserved their sharper questions for Zackery Morazzini, a California deputy attorney general, and interrupted him more often. Justice Stephen Breyer seemed to be most inclined to view the law as constitutional, saying that if asked whether a legislature could reasonably view video games as harmful, "the answer is yes."

Morazzini did say that he believed Postal 2 to be covered by California's law, and Mortal Combat is "a candidate."

And it was Justice Sonia Sotomayor who seemed to be the most conversant with video games, asking whether a video game showing a Vulcan "being maimed and tortured" would be covered by the act (answer: no) and whether an "android computer simulated person" would be covered by the act (answer: no). Justice Antonin Scalia was sharply critical of the law, but on more traditional grounds: saying that "it has never been understood that the freedom of speech did not include portrayals of violence."