Starbucks shortchanged customers on drinks, according to a new putative class action filed in California federal court.

Siera Strumlauf and Benjamin Robles alleged that lattes made pursuant to a standardized recipe that calls for cups to be filled a quarter inch short of the brim leave the drinks "uniformly underfilled." Starbucks sells its drinks in three sizes: tall, or 12 fluid ounces, grande, which is 16 fluid ounces, and venti, or 20 fluid ounces.

But the chain's lattes—including Pumpkin Spice Lattes, Egg Nog Lattes, and Vanilla Lattes, among others—never meet the size representation on the menu, the plaintiffs said. Baristas are instructed to make the drinks from a standardized recipe instituted in 2009. To create a latte, the recipe requires the barista to fill a pitcher with steamed milk up to an etched "fill to" line that corresponds to the size of the customer's order. Shots of espresso are poured into a separate serving cup, followed by the steamed milk from the pitcher, topped with ¼ inch of milk foam, leaving ¼ inch of free space in the cup. "However, Starbucks' standardized recipes for Lattes result in beverages that are plainly underfilled," according to the complaint, as "the etched 'fill to' lines in the pitchers are too low, by several ounces."

The serving cups used by Starbucks are also too small to accommodate the fluid ounces listed on the menu when used in conjunction with its standardized recipes, the plaintiffs added. The grande beverage cup holds exactly 16 fluid ounces, but the standardized recipe requires the cup to be filled up to "¼ inch below the cup rim," meaning the cups do not permit 12-, 16-, or 20-ounce lattes, Strumlauf and Robles claimed.

The company adopted the standardized recipes and "fill to" lines in 2009 in an effort to eliminate barista discretion and cut back on costs, particularly the amount of money spent on milk, an expensive ingredient, the plaintiffs alleged. However, according to the plaintiffs, the "fill to" lines and standardization resulted in Starbucks cutting too much milk. "By underfilling its lattes, thereby shortchanging its customers, Starbucks has saved countless millions of dollars in the cost of goods sold and was unjustly enriched by taking payment for more product than it delivers," the complaint argued.

The suit requests compensatory and punitive damages for violations of California's false advertising law, unfair competition law, the Consumers Legal Remedies Act, fraudulent advertising, breach of warranty, unjust enrichment, and negligent misrepresentation.

To read the complaint in Strumlauf v. Starbucks Corp., click here.

Why it matters: Starbucks released a statement that the claims are without merit. "We are proud to serve our customers high-quality, handcrafted and customized beverages, and we inform customers of the likelihood of variations," the company said.