Walmart Inc. on Thursday sued to prevent a former top tax executive from taking a job with Amazon.com Inc., arguing the move would present a “direct competitive threat” to Walmart by exposing the online retailer’s business strategy and potential merger plans.

The lawsuit, filed in the Delaware Court of Chancery, accused Lisa Wadlin, Walmart’s senior vice president and chief tax officer, of breaching a noncompete provision in her employment contract that bars her from taking a job with a competitor or global retail business for two years after leaving the Bentonville, Arkansas-based corporation.