The case of the shrinking spices involves peppercorns in jars, not just tins of ground pepper, Watkins Inc. claims.

The Winona-based company sued McCormick & Co. earlier this month, alleging the spice giant "deceived" consumers by stealthily slashing the amount of black ­pepper in its tins by 25 percent, without shrinking the container or lowering the price.

Watkins, a small competitor in the pepper business, said Tuesday it will add to its suit, claiming that McCormick cut by 19 percent the content in a popular product called "Black Peppercorn Grinders." The product continues to be sold in the same size jar at the same price, though the amount of pepper has been cut from 1.24 ounces to 1 ounce, Watkins says.

Watkins claims McCormick's content shrinkage violates federal prohibitions on "slack fill." "McCormick is trying to camouflage its improper slack filling in its Black Peppercorn Grinders as it did in their ground black pepper tins, " Watkins said in a statement.

In response, McCormick said in an e-mail, "We will vigorously defend any amendment changes through our legal process. We will not engage in these PR stunts by this competitor." The company has said it reduced the weight of black pepper products after big increases in global pepper prices.

Maryland-based McCormick is the nation's leading spice company, with $4.2 billion in sales last year. Watkins, a 147-year-old company owned by prominent Minnesota businessman Irwin Jacobs since 1978, sells personal care products, food extracts and spices.