(Bloomberg)—Walmart Inc. sued its former chief tax officer for violating her employment contract by defecting to online rival Amazon Inc. to become one of its senior tax executives.

Lisa Wadlin, Walmart’s senior vice president and top tax executive, wrongfully left the Bentonville, Arkansas-based chain last month to move to Amazon’s headquarters in Seattle, Walmart officials said Wednesday in a lawsuit.

“Wadlin’s pursuit of employment with Amazon eviscerates the contractual terms Walmart bargained for’’ in her employment agreement, the chain’s lawyers said in the Delaware Chancery Court lawsuit. Walmart said it was seeking to protect its rights to lawfully restrict “senior employee’s ability to work for its direct competitor.’’

Over the past three years, Walmart has spent billions to revitalize its once-moribund web unit, expanding delivery options, hiring fresh talent and making acquisitions. While sales soared last year, the spending has taken a toll on profitability. When the company reported slowing online growth and disappointing margins during the critical holiday quarter, investors pummeled the stock.

Walmart is No. 3 in the Internet Retailer 2018 Top 500. Amazon is No. 1.