Some of the nation's largest retailers posted weaker-than-expected sales in June as shoppers cut back on spending due to worries about the troubled job market, Knight Ridder reported.

Analysts called the results trouble for the crucial back-to-school shopping season, the industry's second biggest revenue-generating event, which starts next month.

"The bigger picture is worrisome," said New York retail consultant Robin Lewis, who expects back-to-school sales to be flat or decline. "The consumer has been spending less and they are saving more. Manufacturing has been declining. All of this signals decreasing demand."

Worried about unemployment and the European economy, consumers don't want to fill up their shopping carts, analysts said.

As a result, same-store sales at the nation's retail stores increased just 2.6% in June, compared with 8.1% a year ago, according to the research firm Retail Metrics/Bloomberg. That data, which measures sales at stores open at least a year, is a key indicator of a retailer's financial health, Knight Ridder reported.

Thomson Reuters, which polls 20 U.S. retail chains, saw its Same-Store Sales Index inch up only 0.1% in June, far below last year's 6.7% rise for the month. Analysts have said that warm weather may have prompted consumers to make summer apparel purchases earlier than usual, shifting sales from later months like June.

Last month, 28% of consumers said they earned less take-home pay compared to a year ago, according to Britt Beemer, chairman and founder of America's Research Group. That's compared to just 16% in March.

"Middle America is truly being squished in this whole thing," said Beemer, known for his Christian retail channel studies. Shoppers will likely buy only the necessities for back-to-school and defer purchases to the Christmas shopping season, he said.

Three years ago, only 6% of customers bought back-to-school items during the holidays. Last year, that grew to 23% of consumers, Beemer told Knight Ridder.