The U.S. government disrupted the weekend—and life—plans of Cory Albertson and thousands of others like him who earn much of their living playing poker online.

For nearly eight years, Mr. Albertson has camped out every Sunday on his couch with his laptop to play No Limit Hold'Em with thousands of other online players at PokerStars or Full Tilt Poker. He might pocket $500 for the day, or lose money, but sometimes he'd win big, as much as $75,000 at a time, adding a nice sum to his income as a freelance writer in Austin, Texas.

The U.S. Justice Department announced Friday it was blocking players in the U.S. from accessing Full Tilt Poker, along with other online poker sites, accusing 11 people of bank fraud and of illegally operating gambling websites. The government seized accounts run by the sites that held money stored by players.

The crackdown came after years of tension between the sites and the U.S. government, which long held that online gambling is illegal. The case could test the claim by the poker site operators that operating a poker site online isn't illegal because, they say, as a game that involves skill, poker is not gambling.