Updated from 10:49 a.m. EST

SAN FRANCISCO -- The slowdown in U.S. consumer spending has now tarnished Tiffany ( TIF).

Shares of the jewelry purveyor tumbled 12% Friday after the company reported soft holiday sales in the U.S. and trimmed its earnings projection. While difficult comparisons from a year ago were partly to blame, Tiffany said the weakness was worse than expected, fueling concerns that recent consumer troubles aren't limited to lower-income shoppers.

Tiffany's same-store sales, or sales at stores open at least a year, fell 2% in the U.S. for the two-month period ended Dec. 31, as traffic trends weakened. Worldwide, same-store sales were up 3%.

"We entered the holiday season facing well-known, challenging macro conditions in the U.S. and these results reflect it," said Mark Aaron, vice president of investor relations, in a conference call. "Therefore, soft U.S. results were not too surprising, although the magnitude of the softness in our stores and direct marketing sales was more than we expected."

Tiffany's total U.S. sales edged up 4% in the holiday period, while international sales jumped 18%. The company did record a 10% increase in sales at its New York flagship store during the holiday period, as foreign tourists took advantage of the weak dollar.

The flagship 5th Avenue store played a big role in propping up results. For instance, Aaron said on the call that seven of Tiffany's stores just outside of New York City had a combined 10% drop in same-store sales for the period.

The declines in the U.S. come as the housing slump and tightening credit standards have squeezed U.S. consumers. Retailers reported weak traffic for the holidays, while on Thursday high-end card company American Express ( AXP) warned that it saw a significant slowdown in spending in December.

Bear Stearns analyst Randal Konik said Tiffany's holiday sales proved that "no company is immune from a softening retail environment."

Up until now, many luxury brands had been protected from economic concerns. But several of them - particularly those that also attract middle-income customers who have cut back on splurges -- are starting to show cracks. Coach ( COH), for instance, warned in October of weakening traffic at its U.S. stores.

Shares of Coach were also taking hits, falling 7.4% Friday to $26.73. High-end retailers Saks ( SKS) and Nordstrom ( JWN) were down 7.5% and 5.3%, respectively.

Tiffany was down $4.40, or 11%, to $35.92. With the declines, the stock is 37% off its 52-week high of $57.34 reached in October.

Tiffany now expects earnings of $2.25 to $2.28 a share for the year ending this month, before several one-time items. Its prior guidance called for a profit of $2.25 to $2.30 a share.

The new forecast falls below analysts' average target for fiscal-year earnings of $2.30 a share.

Still, some see long-term value in Tiffany, even if short-term results are now showing weakness. Analysts point out that year-earlier same-store sales were up 11% in November and 8% in December, a difficult performance to repeat in a tough economy.

"While the deterioration in U.S. sales against tough comparisons is concerning, we point out that TIF clearly outperformed given its non-promotional stance, which coupled with favorable product mix, should drive solid gross margin improvement," wrote Cowen and Company analyst Lauren Cooks Levitan.

Konik notes that Tiffany still has plenty of growth opportunities abroad, noting that sales in Asia, excluding Japan, were up 24% in same-store sales in November and December. He added that the jewelry category is performing much better than apparel, where economic concerns have had the most impact on sales.